Alarm rings before set alarm time
Smart alarm is enabled (see Smart wake up), so the app is waking you within the smart period, when light sleep is estimated.
If that is not what you expect, disable smart period in Settings → Alarms → Smart wakeup → Smart period for all your alarms, or for one alarm in alarm → Smart period.
You can also try different smart period: shortest period is 5 minutes, longest is 2 hours.
Tags: alarm, smart_alarm