Key Considerations for a 7 PM - 3 AM Schedule:

Sleeping from 7 PM to 3 AM
provides 8 hours of sleep, which is adequate, but this schedule—often termed advanced sleep phase—can cause social jetlag and reduced sunlight exposure. It is generally not inherently unhealthy if consistent, but it may conflict with social schedules and can stem from, or cause, early morning awakenings due to cortisol rhythms or melatonin depletion. 
Key Considerations for a 7 PM - 3 AM Schedule:

    Circadian Rhythm: Your body may naturally prefer an earlier bedtime, or you may be forcing a rhythm that causes a 3 AM awakening.
    Lifestyle Impact: This schedule can lead to social jetlag, making it hard to participate in evening activities.
    Benefits: This routine often allows for high productivity in the quiet early morning hours.
    Tips for Success:
        Light Management: Use blackout curtains for evening sleep and seek morning sunlight to stabilize your rhythm.
        Routine: Maintain consistency, even on weekends.
        Environment: If you live in a noisy area, use earplugs or white noise machines. 

Why You Might Wake Up at 3 AM:

    Cortisol Rhythm: Cortisol levels naturally start to increase between 2 and 3 a.m., which can wake you if you are already under stress.
    Melatonin Drop: If you go to bed very early, your melatonin levels may drop too early, causing you to wake prematurely.
    Internal Clock: You may have a naturally advanced sleep phase, meaning your brain is programmed to sleep earlier and wake earlier. 

If this schedule causes excessive daytime sleepiness or interferes with your life, consider gradually shifting your bedtime later by 15-30 minutes every few days.