I'd assume that each destroyer of the same class has basically the same fighter-bay design, as well as internal design. I think the fighter-bay "shields" are force-fields... contain the gases inside the ship. Flying towards them, I think it's possible that your ship is negatively charged so a "bubble" can form--letting you leave the bay.
There is artificial-gravity on Terran ships at least and the reason it takes so long to launch support fighters is that they need to have the pilots wake up/be contacted, report to their correct area for suiting, suit-up, get briefed quickly, choose a ship, customize ordinance, and do the same for the wingmen (if applicable), have all ships properly set-up, get into the ship, strap in, do a system diagnosis (to make sure everything works), power up life-support, power up secondary systems, warm-up engines, receive launch clearance, launch, and possibly receive coordinates to jump to!
That entire task takes a long while when you are allowed to customize your ship to the extent allowed... if you had every pilot suited-up and ever ship powered up and ready, it would probably take 2 minutes. In the above example, more likely 10-15 minutes. If Command expects the need for support, they'll have other pilots and their respective ships ready. Remember that we've flown back-up occasionally... we jump in after the real mission has started, meaning we were the reinforcements.