Hi guys
Each map has a timelimit, and once that timelimit is reached the map changes (like in BF1942 if you had a timer) Possibly could remove the time limit, but not sure if all of the maps have round limits or not (they should have as its a map specific thing to have timers or round limits on them).
Another option which should be in place now as I turned it on the other day, was automatic map voting when there was 2 mins remaining where you can vote to extend the map or change in 2 mins to a new map. (see what gonzo said above)