TaskNearby may be a good option for you, because it
has reminders that are defined with text, a latitude/longitude chosen on a map and a radius;
has intelligent battery optimization;
While not a specific software recommendation, your requirements are met by tons of apps called "calendars" having a feature called "reoccuring events". They'd not only let you define a start date and ...
The opensource system that I recommend is LibreBooking - the free version of BookedScheduler.
It can handle most kind of resources.
It is multi-user.
It has start/end reminders.
It can show calendar ...