Nothing at first. After finding I couldn't create PM meetings, I tried setting the time zone and it didn't seem to do anything. After logging out and logging back in though, the time zone may have taken effect, but I still can't make events in the PM.
If I drag an event from the AM to the PM, it seems to stay in pm though.
Also, if I change a meeting time from 1am to 1pm, the form says that there was no change and won't let me submit; this was for creating meetings iirc. I think their not reading the am/pm part of the form.
If it works for you however, I wonder if its my browser? I tried it in both brave and firefox though, same result