I'm paid hourly, but my hours are weird and somewhat flexible.
I usually get there 15-30 minutes early. That gives me time to take a bathroom break, get a cup of coffee, and [censored] with whoever I happen to run into a bit.
At the same time, it's not unheard of for me to walk in the door and find out something needs urgent attention that only I can fix(or in some cases other people who could don't want to do it). When that happens, I go on the clock the second I walk in.
Also, there are a few days a week where I'm not scheduled to go to work until 11:30. On those days, it's not uncommon that something "urgent" comes up in the morning and I get a call or text about it. Per my supervisor, I'm allocated 15 minutes or the actual time(if longer than 15 minutes) to deal with each occurrence.
As a result of all of the above, I often end up accumulating OT hours. My standard week is 37.5 hours. I have an agreement that I don't need to ask to go up to 40 hours, but anything beyond that goes into time and a half and I have to get approval for that. Depending on the circumstances, I'll either leave early one or two days to keep my time below 40 hours, or just go ahead and get the time and a half. I can't make that decision on my own, though.