I set up an alarm (using Google Now) for 55 minutes, so the end time was around 20:13 (and therefore the start time was 19:18

When I looked at the alarm notification, there's another little number in the right hand side which said 19:43 (so 30 minutes before the time the alarm was set for)

It would make sense if it was the start time (19:18) but by itself it makes no sense.