Version: (using KDE KDE 3.5.7) Take a look at "before the start". It is almost immediate question -- start of what? I can only guess it is start of KDE, but it is better to say it explictly.
Before the start of the appointment of course.
While "of course"? I am used to collective reminder -- so it tells you once about all events (what you have to do in one day), not each time per each event. And why it is invalid? Is it really harm to change words: before the start -- before the event? or anything to make this dialog more clear? This is minor change of course, but useful (since there is no help and no what's this). But I was wrong in saying about start of KDE -- before start does not make sense :-))
Thhis has been fixed for the KDE 4.4 release. The combobox has the choices: before the event start time, after the event start time; before the event end time; after the end time. similarly if the alarm is for a todo, the choices are: before the to-do start time; after the to-do start time; before the to-do due time; after the to-do due time I think this is enough.