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For most travelers, beginning 2–3 days before departure produces the best results. This gives your circadian clock time to begin shifting before you arrive, reducing the mismatch you feel on landing day.

For short trips (1–3 days), it may be more practical to stay on home time rather than attempt adjustment — Time Transit can recommend this when appropriate based on your itinerary.

For long-haul eastward travel across 6+ time zones, beginning 4 days in advance is ideal. The app will calculate the optimal start date for your specific route.

To generate your protocol, Time Transit needs:

• Departure city and destination city (for timezone calculation)
• Departure date and arrival date/time
• Your usual wake time and bedtime at home (or grant HealthKit access so the app reads this automatically)
• Chronotype — are you a morning person, evening person, or neither? A quick questionnaire takes 60 seconds

Optional but helpful: flight departure and arrival times, and whether you have meetings or commitments on the day you arrive.

Yes. Westward travel (a phase delay) is generally easier than eastward travel (phase advance) because the body's natural circadian period is slightly longer than 24 hours — making it easier to push sleep later than earlier.

Time Transit generates protocols for travel in both directions, with direction-appropriate light and darkness timing, melatonin use, and meal adjustments tailored to whether you need to advance or delay your clock.

The current version of Time Transit is optimized for international travel across time zones. Shift work adjustment involves a different class of problem — adapting to a recurring non-24-hour schedule while living in a society synchronized to day-night cycles.

Shift work support is on our roadmap. If this is important to you, let us know at support@timetransitapp.com — user interest helps us prioritize features.

Dim Light Melatonin Onset (DLMO) is the point in the evening when your pineal gland begins secreting melatonin under dim lighting conditions. It's considered the gold standard marker of circadian phase in sleep and chronobiology research.

DLMO typically occurs about 2 hours before your natural sleep onset. Knowing your DLMO lets us time light exposure and melatonin precisely to shift your clock in the right direction — light before DLMO causes a phase advance (earlier), light after DLMO causes a phase delay (later).

Time Transit estimates your DLMO from your self-reported or HealthKit-derived sleep timing and chronotype, then uses this to anchor all protocol recommendations.

The human circadian clock has a natural period of approximately 24 hours and 10–20 minutes — slightly longer than a solar day. This means our bodies naturally drift toward later sleep times without external correction.

Eastward travel requires a phase advance — you must shift your clock earlier (against its natural tendency). Westward travel requires a phase delay — shifting later, which aligns with the clock's natural drift. Physiologically, delay is easier and faster.

Eastward travel across 6 time zones can take 5–7 days to fully adjust naturally. Time Transit's structured protocols compress this to approximately 2–3 days by strategically using light, darkness, and melatonin to accelerate the advance.

Yes. Time Transit's protocol is grounded in decades of circadian science. The algorithm draws on research including:

• The Kronauer-Jewett circadian rhythm model (Harvard Medical School) for mathematical clock simulation
• Phase Response Curves established by Czeisler, Khalsa, and colleagues at BWH/Harvard
• Melatonin phase-shifting research by Lewy, Sack, and the Oregon Health & Science University chronobiology group
• Meal timing and peripheral clock entrainment research from the Salk Institute

A full bibliography and explanation of the algorithm is available in our published whitepaper.

A Time Transit protocol is a day-by-day schedule of precisely timed interventions. Depending on your route, this typically includes:

• Light exposure windows — when to seek bright outdoor light or use a lightbox
• Darkness windows — when to avoid bright light and use blue-light-blocking glasses
• Melatonin timing — low-dose (0.5mg) melatonin taken at the phase-appropriate time
• Caffeine cutoffs — when to stop caffeine to avoid interfering with sleep onset
• Meal timing adjustments — shifting meals to signal the destination timezone to peripheral clocks
• Adjusted target sleep times — progressively moving your bedtime toward the destination

Partial adherence is still beneficial. The interventions in your protocol are ranked by impact:

• Highest impact: Light exposure and darkness timing (prioritize these)
• High impact: Melatonin timing
• Moderate impact: Sleep timing adjustments
• Supporting role: Meal timing and caffeine management

If you can only do one thing, prioritize the light and darkness windows. Even partial adherence to the light protocol will noticeably reduce jet lag compared to no intervention at all.

Yes, but your protocol will be calibrated differently. Evening chronotypes (night owls) have a naturally later DLMO — typically 11pm–1am versus the 9–10pm range of intermediate types.

Time Transit accounts for your chronotype when estimating DLMO and generating your light/darkness windows. Your protocol may look different from a morning person's protocol even for the same destination, because the phase response curve has different characteristics relative to your baseline phase.

For eastward travel, night owls may find the protocol more challenging, as phase advancing is physiologically harder for later chronotypes. The app will be realistic about this and provide a graduated schedule that's biologically achievable.

Effective light exposure for circadian shifting requires sufficient intensity. General guidelines:

• Outdoors on a sunny or overcast day: Excellent. Even overcast outdoor light (1,000–10,000 lux) far exceeds indoor lighting.
• Light therapy lamp (10,000 lux): The clinical standard for controlled light therapy. 20–30 minutes is typically sufficient.
• Bright indoor office lighting: Marginal (300–500 lux). Usable if outdoor access isn't possible, but less effective.
• Phone or tablet screen: Insufficient for meaningful phase shifting. Not a substitute for bright light.

During "seek light" windows in your protocol, prioritize outdoor exposure where possible. Walk, have your morning coffee outside, or eat near a window. If traveling in winter or arriving at night, a light therapy lamp is a useful investment for frequent travelers.

On aircraft, "avoid light" windows mean minimizing light exposure from all sources:

• Close the window shade
• Wear a sleep mask
• Dim your device screen to minimum or turn it off
• Blue-light-blocking glasses (amber-tinted) are effective if you need to use a screen
• Avoid the overhead reading light if possible

Cabin lighting on many airlines is already managed for time-of-day comfort, but this may not align with your personal protocol. Bringing an eye mask and amber glasses gives you full control regardless of cabin conditions.

Research consistently shows that low doses (0.5–1 mg) are more effective for phase shifting than the 5–10 mg doses common in consumer products. Higher doses cause sedation but minimal additional phase shifting, and can cause grogginess the next morning.

Time Transit recommends 0.5 mg when melatonin is part of your protocol. This dose is sufficient to shift circadian phase and mimics the physiological timing and magnitude of natural melatonin secretion.

If you can only find 3 mg or 5 mg tablets, splitting them or using a liquid formulation gives more precise dosing.

Caffeine works by blocking adenosine receptors in the brain. Adenosine is the sleep-pressure molecule — it accumulates during wakefulness and promotes sleep onset when levels are high. By blocking it, caffeine keeps you alert but doesn't reduce adenosine itself.

Caffeine's half-life is approximately 5–6 hours, meaning half of a dose is still active 5–6 hours after consumption. During jet lag adjustment, you're trying to shift your sleep onset time — residual caffeine that suppresses sleep onset at the wrong clock time directly undermines the protocol.

Your cutoff time in the protocol is calculated from your target sleep onset in the destination timezone. Earlier cutoffs may apply when you're attempting to advance sleep significantly.

No. Once your protocol is generated, Time Transit works entirely offline. All calculations happen on-device, all data is stored locally, and notifications are scheduled locally. The app will work on a plane in airplane mode.

An internet connection may be needed initially to download the app and to look up timezone data for unusual destinations, but your active protocol requires no connectivity.

Go to iPhone Settings → Health → Data Access & Devices → Time Transit. Here you can individually toggle access for each data type the app has requested.

You can also manage this within the app under Settings → Health Data. If you revoke HealthKit access, the app will continue to function using manually entered sleep and wake times instead of HealthKit-derived data.

Yes. You can create and store multiple trip protocols in Time Transit. Each trip generates its own protocol, which can be set as active when you're ready to begin that journey. Past trip protocols are saved in your trip history for reference.

Notification issues are usually one of a few causes:

• Notifications disabled: Check Settings → Notifications → Time Transit. Ensure "Allow Notifications" is on and Time Sensitive Notifications are enabled.
• Focus Mode: iPhone Focus modes (Do Not Disturb, Work, Sleep, etc.) can block notifications. Either allow Time Transit as a permitted app in your Focus settings, or set notifications to "Time Sensitive" — which bypasses most Focus modes.
• Low Power Mode: iOS may delay non-critical background activity in Low Power Mode. Time Transit uses local notifications which should fire regardless, but check if this correlates with your issue.
• Incorrect timezone: If your iPhone timezone hasn't updated to match your destination, protocol notifications may be off by the timezone difference. Ensure automatic timezone is on: Settings → General → Date & Time → Set Automatically.

Time Transit reads your current timezone from the iOS system clock rather than your GPS location, so it doesn't require location permissions. If timezone detection fails:

• Go to Settings → General → Date & Time and ensure "Set Automatically" is toggled on
• If you're traveling and the timezone hasn't updated, you can force an update by toggling Set Automatically off and back on
• Alternatively, manually select your current timezone in the same settings screen

You can also manually set your current timezone within Time Transit's settings if you prefer to override the system value.