Reminders time delay presets are inflexible
GNOME Calendar offers me only a limited choice of reminder times: 5, 10, 30, 60 minutes and 1, 2, 3, 7 days. That's quite inflexible and like offering me the choice between a trip to the grocery store and a trip to Pluto.
Pretty much every other calendaring app I've encountered usually just asks me what time unit and what value I want, offering the choice between minutes, hours, days and what number to put in.
The 5/10/30 mins notification kinda works for the typical "I need a reminder to walk to the next room for a meeting" scenario, but it doesn't handle any more sophisticated usecase, such as "I have some event starting early tomorrow morning and I want to be notified on the evening before so that I can remember to prepare materials for it or to go to bed early" or the "I have a meeting but I need to take the car/helicopter and drive/fly 45 minutes to get there"...