Stage Time Limit is 30 minutes



I've been looking around for days now and cannot find anything speaking of the total time limit of stages. I've been playing RBR for 5 (or is it 6?) years and never realized the game goes to "replay,restart,quit, etc..." screen after 30 minutes.
I found this out after testing my 45 Kilometer track and I got to milepost 42 , and it stopped (30 minutes). The question is: where is the switch to make it unlimited time?