So, at least 30 seconds, I guess?
As said, rather make it configurable. This is a real-world system… 😄
There are some public calendars (like concerts events) that don’t have reminders and you can’t control the source, so it is impossible to set a reminder for now. For those it would be super helpful if you can set some fixed reminders (yes, more than one ideally) for all events in a particular ICS calendar. So I can set to get reminders for all concerts the day before and 2 hours before the event for example.