Adventuring is rarely that busy, but sometimes it's busier. Remember, adventuring parties are special ops / Navy Seals in a lot of cases, you can't always guarantee a mandated 1 hour lunch break from your union rep when Vecna is about to ascend.

Nova-ing two fights in a row isn't a big deal, that's a strategic choice on the part of the players. It might work out in their favor or it might not, just like stopping for an hour-long SR might work out in their favor or not.