Okay. This is somewhere between looking for rules references and seeking advice.
On a narrative scale, for a single PC, launching a fighter involves getting on board (a personal scale manoeuvre unless you have Let's Ride!) and powering it up (probably a second manoeuvre), and then on a ship scale, accelerating (a manoeuvre to speed up) and moving from the area of the launch bay to 'free space' (a fly manoeuvre).
That's a total of four manoeuvres - so 2 turns for a generic minion, or 1 turn for a PC with Let's Ride! who's prepared to burn some strain.
For a group of minions - or multiple groups of minions - this becomes a little more....abstract.
A militarised Gozanti carries 4 TIE fighters on external racks. Launching all four at once is not especially unrealistic (although doing it in pairs seems safer to avoid the possibility of collisions).
A proper Imperial navy Carrier or Destroyer carries well over a hundred fighters. Launching all of them through a single bay in one round seems a little over the top.
Is there some advice on this in Stay On Target or Lead By Example that I've missed? How long would you expect a Destroyer at Battle Stations to take to clear the decks?