When launching from a space station the fastest way to get into super/hyper cruise, especially in a big and heavy ship, is to boost out of the mail slot (may need 2 boosts for some ships) to get that max speed. Next you need to turn flight assist off and position your ship to face your target. As soon as you clear the mass lock zone, re-enable flight assist, hit boost and spool up your FSD - you will be out in no time!
Boosting grants buff to RCS thrusters so initiating FA off flip after boost makes it very responsive - again, especially in chunky ships. The Mass lock ambit is close enough so that ship won't loose too much of the speed by the time it reaches it - and hitting the boost and enabling FA right after puts even the largest ships firmly on track.