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What you're experiencing is a classic circadian rhythm disruption. Your body's internal clock (the circadian pacemaker, located in the brain's suprachiasmatic nucleus) was calibrated to sleep from ~1–2 AM to 9–10 AM. Shifting to 10 PM–6 AM is a roughly 3-hour phase advance — and the pacemaker doesn't instantly shift with you. The result: your biology still wants to be awake at 10 PM and asleep at 6 AM, creating a mismatch that causes sleepiness during your new wake hours and difficulty fully sleeping during your new sleep window.

This is the same mechanism as "social jet lag" — Harrison's defines it as when bedtimes/wake times shift 3–4+ hours between days, causing delayed circadian phase, excessive daytime sleepiness, and poorer performance.

Most circadian adjustments of 2–3 hours take about 1–2 weeks to normalize, assuming you hold the new schedule consistently. Reverting on weekends or days off resets the clock backward and restarts the process — this is the biggest reason people stay stuck.

Wake time is the strongest anchor for your circadian clock. Do NOT sleep in on weekends. Even if you sleep poorly, get up at 6 AM every day. This is the single most impactful intervention.

Morning light (ideally outdoor sunlight, or a 10,000 lux light therapy lamp for 20–30 min) is the primary signal that advances your circadian phase earlier. Using it right after 6 AM will push your internal clock to align with your new schedule faster. — Harrison's Principles of Internal Medicine 22E

After ~8–9 PM, dim indoor lights and use blue-light filters on screens. Evening light signals your clock to stay awake later, directly opposing the advance you're trying to make.

Low-dose melatonin (0.5–3 mg) taken around 8–9 PM can help shift your clock earlier. It works best when your endogenous melatonin is still low (i.e., during the biological daytime). Higher doses are not more effective for circadian shifting. — Harrison's Principles of Internal Medicine 22E

A brief nap (10–20 min) in the early afternoon can blunt sleepiness without significantly disrupting night sleep. Avoid napping after 3 PM.

Caffeine can help alertness during the early adjustment period, but avoid it after 2–3 PM as it will erode the quality of your 10 PM sleep. It cannot substitute for full adaptation. — Harrison's Principles of Internal Medicine 22E

Instead of jumping straight to 10 PM, you can shift bedtime earlier by 15–30 minutes every 2–3 days. This gentler approach reduces daytime sleepiness during the transition.

The sleepiness is temporary — it reflects your biology catching up to your behavior. Consistency with the new schedule, morning light, and evening melatonin are the three most evidence-based levers to accelerate adaptation.

If the sleepiness persists beyond 3–4 weeks despite strict adherence, it may be worth considering a formal evaluation for an underlying circadian rhythm disorder (such as Delayed Sleep-Wake Phase Disorder), where the biological clock has a structural tendency to run late. — Harrison's Principles of Internal Medicine 22E; Adams and Victor's Principles of Neurology, 12th Ed.