Ok there's a problem with this. Adding the logic_arena entity causes the game to ignore the timer. Is it maybe possible to set a trigger to make the game end when a timer running in the background hits a certain time?
edit: Ok, If I can figure out how the CP's entities for round-end works, I think I can leave those in, along with a timer that activates them.
However, I don't even see anything with the timer atm. The only options are "random interval" related. That doesn't sound like what I need at all. The team_round_timer seems to be ignored entirely when using the arena logic, so I need to find something else.