Summary: I want reminder options for fixed times of day (like there is for all-day events) for all type of events.

This suggestion https://appgenix.uservoice.com/forums/280499-business-calendar-2-open/suggestions/8941996-set-event-reminders-time-as-date-and-time-for-ex was implemented for all-day events.

For events with a specific start time, it isn't of much use to have a reminder more than say 2 hours before expressed as "X hours before". E.g. "8 hours before" is often in the middle of the night. Much more useful would be something like:

10 minutes
20 minutes
30 minutes
1 hour
2 hours
08.00 same day
20.00 day before
13.00 day before
08.00 day before
08.00 2 days before
08.00 3 days before

Ideally, which options there are should be customizable.

To elaborate, I find that there are conceptually two types of reminders. One is "get started" and goes off soon before the event, with only as much time as it takes to get ready. For this, "30 minutes before" is the right type of reminder. The other is "prepare for upcoming event", and that is often to pack or prep the day before. For this you want to pick a clock time that is typically a good preparation slot, maybe 09.00 for work related events, or 20.00 for private events, pretty much regardless of the event time.