Jet Lag App with a Personal Light and Sleep Plan

The body clock shifts fastest when bright light hits your eyes at the right times — and stays stuck when light hits at the wrong times. A jet lag plan schedules light exposure, darkness, and sleep around your specific flight so the shift starts before you even board. Sundial computes that schedule for your exact route and shows you what to do hour by hour.

Yes. Sundial's circadian engine runs entirely on your iPhone, so the full schedule works in airplane mode over the ocean. Nothing about the plan needs a server, which matters most exactly when you have no wifi at 38,000 feet.

Your circadian rhythm is the internal clock that times sleep, alertness, and hormone release to roughly a 24-hour cycle. Crossing several time zones in a day moves the sun without moving your clock, so your body keeps running on home time. A light-and-sleep schedule like Sundial's re-anchors that clock to your destination.

It depends on your direction of travel, how many zones you cross, and where your body clock currently sits — light at one hour advances the clock and the same light a few hours earlier delays it. That asymmetry is why generic advice fails. Sundial does the math for your specific trip and paints the seek-light and avoid-light windows on a timeline.

Starting a day or two before departure usually makes arrival day far easier, because your clock is already partway shifted when you land. Sundial's plan covers the days before, during, and after the flight, so the pre-shift happens in small, livable steps.

Yes — eastward travel is usually harder because it asks your body clock to advance, and most people's clocks drift long, not short. A good plan treats the two directions differently. Sundial picks a phase-advance or phase-delay strategy based on your route and zone count, including the wrap-around cases past twelve zones.

In Sundial you just edit the departure or arrival time and the entire schedule recomputes locally in seconds. There is no support ticket and no waiting on a server — a delay is a two-tap correction, not a broken plan.

Yes. Sundial supports multi-leg trips and refueling stops, computing the plan across the whole journey rather than treating each leg as a separate trip. You enter the legs manually, so unusual routings work fine.

Melatonin timing matters more than most people expect — taken at the right point it nudges the body clock in the direction you want, and at the wrong point it can work against you. Sundial can optionally show when timing would help for your specific plan. It shows timing information only, not dosage, and it is not medical advice — talk to a clinician about whether melatonin is right for you.

Some do, and worse, some send pushes that contradict the in-app plan. Sundial's notifications are optional and dismissible, and they are generated from the same single schedule you see in the app, so the nudge and the plan always agree. Turn them off entirely and the Today card still tells you everything.

Yes. With your permission, Sundial reads recent sleep from HealthKit to estimate your baseline rhythm, so the plan starts from how you actually sleep rather than an assumed 11-to-7. The read is opt-in and the data stays on your device.

No. Sundial is a personal travel-planning aid for passengers, and it must not be used to schedule sleep or alertness for on-duty pilots, drivers, or anyone in a safety-critical role. Duty scheduling is governed by regulations and professional fatigue-management systems.