On Mondays I start work at 12midnight sunday to 830am monday, then I come back at 10pm monday until 430am tuesday. The 2hrs I work on monday should that be considered OT or does it go towards my tuesday workday which starts at 10pm monday.

Here is the work schedule

Monday: Start monday 12am -830AM
Tuesday: Start 10pm monday - 630am tuesday
Wens: Start 10pm tuesday - 630am wens
Thurs: Start 10pm wens -630am thurs
Fri: start 10pm thurs -630am fri.

Your employer can define the workday in any way they see fit, as long as it does not change in order to avoid overtime. In this case, they would likely define the workday to be Noon-to-Noon rather than Midnight-to-Midnight. This would avoid any daily overtime given this secudule. (Assuming you take a 1/2 hour meal break).

Your employer can define the workday in any way they see fit, as long as it does not change in order to avoid overtime. In this case, they would likely define the workday to be Noon-to-Noon rather than Midnight-to-Midnight. This would avoid any daily overtime given this secudule. (Assuming you take a 1/2 hour meal break).

Can the employer define the workday for each individual employee or does the workday have to be the same for everyone company wide?

Theoretically, it could be different for everyone, but that would be a nightmare for the employer to adminster. They cannot change the workweek definition unless it is intended at the time to be a permanent change, and they can't change it back and forth to avoid paying overtime.