Alternate solutions

Lock Picking. When Thief is added, or thief traits, which ever comes first. They could pick the lock instead of fighting the jailer NM. This could potentially save you a lot of time saving a party member. Though there should be a downside to it as well.

Picking the lock should be a small mini-game much like the DoL mini-games. Hitting a precise point into the chamber of the lock. f you fail you know fight the NM with adds. The number of add is half of what the number of your team is.

Party of 8 saving 1 party member with a lock pick and fails = NM Jailer with 4 Monsters.
Party of 8 saving 4 party members with a lock pick and fails = NM jailer with 2 Monsters.

The Fastest way to free them shouldn't always be the best action.

So Fight the Jailer himself, or pick the lock.