I don't see much of a point in questioning the motives of anyone in 
need of a "on-time reminder". All other PIM applications that I am 
aware of support this, and so does the iCalendar standard.

An "on-time reminder" might be useful e.g. for phone calls that need 
to be made at a certain time when the called party is available. Most 
likely you don't need to place that call at the very second of the 
event's time as entered into your calendar?a few minutes in won't hurt 
anyone. So an on-time reminder would be fine. Of course one could 
argue that a phone call would be something that ought to be put into 
the task list rather than the calendar. But to me, that kind of 
argument is pretty much on the "you're holding it wrong" track. If 
people want that in their calendar, why not let them?

Or suppose you're in a office setting and want to put a reminder into 
your calendar for an appointment that will take place in your office 
where a coworker is supposed to join you. If he shows up a few moments 
early, he will interrupt your work by knocking on your door, you will 
have your meeting, and all is fine. But if he's not there on time, you 
might want to have a reminder to call him at the scheduled time.

I'm sure one could think of many more occasions where reminders at the 
time of an event's start time are appropriate, e.g. a working 
environment with less strict punctuality rules where everyone is used 
to meetings really starting five minutes past the hour when the 
nominal start is on the full hour spot. But still, that's not really 
the point here. The point is that on-time reminders for calendar 
events are a common thing and that Kronolith should support this.

I wonder what the usecase is for such an alarm.

With a reminder set at 0 minutes before an event, you'll be either too 
late for your meeting (it starts at the moment you receive the alarm) 
or you're already in the meeting (and it serves no purpose anymore).

The only thing that would make sense to me is that Kronolith should 
not accept 0 as input here.

I will look into this if I can reproduce in my current version.

Hi,

Setting reminder to 0 minutes (this can be done with some clients, 
e.g. Lightning and Android) for events makes the event be saved in 
kronolith but reminder not set, silently discarded.

Expected behaviout: 0 minutes reminder allowed, or if not, throw any 
error or warning.

Regards,
Carlos Velasco