Tablet turns itself ON at a specific time when in cradle

My Tab 4 turns itself on every night at specific time. I cannot figure out why, or what setting may be the culprit.

Every evening, I tap the power button to "sleep" my tablet before I put it in its cradle to charge. However, every evening at a specific time the tablet display lights up showing the lock screen, which wakes me up. This is making me nuts! I can't find any setting that would affect this behaviour, and there are no alarms set to "wake" the tablet at some specific time.

Any ideas where I should check?