We have a fairly significant issue with Arduino events at the moment. In short, if you create two (or more) of them for the same widget before the time that the first one is supposed to fire, the second (and 3rd, 4th) one will never fire.
For example, using a digital pin and a light switch widget, and assume it is 14:30.
If at 14:30 you create an ON event for 14:45, and an OFF event for 15:00, the OFF event will never fire.
If at 14:30 you create an ON event for 14:45, then wait until 14:50 to create the OFF event for 15:00, the OFF event will fire OK.
So while Arduino scheduling isn't entirely broken, it's fairly limited by this bug. We're working on it and I've added you to a list to update when a fix is in place.