In the persistant campaign that I was working on, here is the rules we used.

When a ship reveals a navigate dial, it may instead of performing the command, discard the dial to declare it is calculating a hyperspace jump. The ship then may attack and move as per normal this round.

At the beginning of it's next activation, instead of revealling a command dial, the ship may immediately be removed from the play area (having jumped to hyperspace).

If the ship takes any actions instead, then it remains in play as normal, it's calculations are deemed void and it needs to begin the process all over again.

Edit - by basing it on commands it meant that smaller ships are able to respond (and leave) much more quickly than larger ships that might take 2 or 3 turns to be able to flee a battle.

Squadrons with hyperdrives could calculate a jump by spending the ability to shoot to calculate their jump. (This means that on their own they cannot move or shoot, or with a squadron command, they can still move, but cant shoot). The next time they activate they jump out, or as with ships, can decide not to jump but have to start over again if they want to leave.