I think in real life you'll have 350sec to use DRS where ever you want. We don't have a time limit. So DRS is always available.
In the league, DRS is only available in the DRS zones. In practice, Quali and the race as usual within a 1-2 sec gap.
I'm still a bit confused, does a track need a DRS zone built into it for DRS to work like we had at Hockenheim ? and if it does has Sebring got a DRS zone.