What I hate in the default calendar is that

you can set the the events only at prefixed times, I mean every 5 minutes, at ex. at 10.15, at 10.20 etc,

than you can set the alarm 5 min before, 15 min before etc.

and at least repeating every day, week, month or year.

This may be good, because you don't always input manually the numbers 1+5 at ex. for 15 min, but sometime i want more personalisation like

event at 10.28 exact, alarm at 10.27 exact and repeat every two weeks at ex.