Free, no signup, nothing leaves your browser. It answers two questions: how much your weekend sleep shifts your body clock, and which bedtimes fit the time you need to wake up.
Social jet lag is the gap between the middle of your sleep on workdays and on days off. A gap of 2 hours is roughly like flying two time zones every weekend, which is why Sunday night feels impossible. The most common fix is to keep your wake time within about an hour every day and get daylight soon after waking.
Bedtimes are counted back from your wake time in roughly 90-minute sleep cycles, plus about 15 minutes to fall asleep. Cycles vary from person to person, so treat these as starting points, not rules. Most adults need 7 or more hours.
This is general information, not medical advice. If you have ongoing insomnia, loud snoring or daytime sleepiness, talk to a doctor.