It depends on bombing conditions. If I have plenty of time to plan then yes the door get opened way in advance so my speed has time to stabilize.
If I have to do a last minute course correction, or get attacked while calibrating and am rushed.. then sometimes I only get one or two calibration attempts in before crunch time. If my calibration is a few MPH faster than my actual speed, I can close my bomb doors to gain a few MPH and then right as I'm ready to drop I open them, drop the bombs, and close them again real quick.
Yes in a way this may be 'gaming the game' but it does come in handy during times when calibration may be less then perfect and there is no time to get it right.