The Clock is a mechanic in the game as it keeps track of the time inbetween 12AM and 6AM. 

The Clock has a red digital number layout which has AM to the left, and only the hour numbers, no minutes or seconds. 

The Clock is also known to be on the desk in the Office next to the lamp and the monitor, checking the Clock on the desk is the only way to check what time you are on so you know how far you are from 6AM.