Singapore → San Francisco

Jet lag is the mismatch between local time in San Francisco and the clock your body is still running from Singapore. An advance asks your body to become sleepy and wake earlier. JetLagPlan models the shortest useful phase shift rather than blindly treating the printed UTC offset as the amount your body must move. Local clocks are 15 hours apart, but your body does not need to move through that full distance. On a 24-hour circadian clock, the shorter adjustment is 9 hours in the advance direction. A reasonable planning estimate for this route is around 9 days of adjustment, with individual response varying by sleep history, light exposure and schedule.

Morning light is the main reset signal for an advancing plan. Aim for useful outdoor light after waking in San Francisco, then keep the late evening comparatively dim so you do not push the clock back in the opposite direction.

If your schedule allows, begin 3 days before departure. Move your normal bedtime and wake time 30–60 minutes earlier each day and reinforce the change with bright light after waking. Partial preparation still helps; do not sacrifice a full night of sleep simply to chase a perfect schedule.

Switch your reference clock to San Francisco time at boarding. Sleep when it is night at the destination rather than simply sleeping whenever you feel tired. Use darkness, an eye mask and earplugs to protect that sleep window, stay hydrated and keep alcohol low or avoid it.

Your first strong reset signal in San Francisco should be morning light. If you arrive during the morning, use outdoor light after landing. If you arrive later, stay on local time and make the next morning your first deliberate light window. Avoid a long late-day nap that makes the local bedtime harder to reach.