Exactly what’s just happened to me today, just not in the “early morning hours” but at 16:00.
I had the clock alarm set at 16:00. That time has just passed without any alarm or any other reaction whatsoever, and in the Clock application the alarm remained active as if the time didn’t come yet. Between 16:00 and 16:10 absolutely nothing happened.
Then, 10 minutes later, at 16:10, a notification was SILENTLY shown on the Events screen that there is a SNOOZED alarm.
Then, yet another 10 minutes later (i.e. 20 minutes past the correct time) the (allegedly snoozed) alarm went off.
Which means that as of 4.5.0.19 the Clock alarm functionality became TOTALLY UNRELIABLE. Along with Calendar alarms, which are also broken as reported here.