Samsung
Default Reminder Time for Calendar Events auf Samsung
Samsung Calendar applies a fixed alert whenever you create a new entry: 10 minutes before for regular events, and 5 p.m. the day before for all-day events. This behavior comes from the app's own alert settings, not from the general system notifications, so it stays the same across Android and One UI updates unless you change it manually.
If you find yourself editing the reminder time on almost every event, adjusting the default saves that repeated step. The setting applies going forward to newly created events; entries you already saved keep whatever reminder they had at the time.
Change the default reminder
Open Tap on Calendar ➔ Open the Menu ➔ Tap on Settings ➔ Tap on Alert settings. From there, pick Choose Events or All-day events depending on which default you want to change, then Choose an option from the available time intervals.
You can set separate defaults for regular events and all-day events, since they are two independent options inside Alert settings. If a specific event needs a different reminder than your default, you can still override it while creating or editing that single event without affecting the general setting.