I once shocked a former bandmate by starting a full 6 string change 15 minutes before showtime.
He figured I was crazy! That I wouldn't be done in time, and I'd be out of tune during the show with new strings.
I was on time and in tune
He was an experienced bass player but had never seen me change strings and pre-stretch.
(EDIT - this was a Strat with stock trem, bone nut and locking tuners)
Here's how I do it:
After the strings are on and tuned roughly to pitch:
Hold down the string at the 12th fret, grab the string halfway between 12th and bridge with your other hand and rapidly yank it back and forth about 30-40 times. Tune up to pitch again, grab between the nut and 12th fret this time and yank it back and forth another 30-40. Tune up to pitch again, repeat for all strings. It sounds like a lot, but the whole process takes me less than 5 minutes. I can yank up and down really fast (lol.. don't go there..
)
When I say "grab the string", I mean hold it between thumb and first 2 fingers to really grab hold of it, because you have you apply quite a lot of pressure and bend it out pretty far to either side for effective stretching. When I first started doing this I managed to break a few high E strings.. be careful, but DO pull them pretty hard.
The wound strings stretch out way more than the unwound, but after doing this routine and tuning up I find they all stay in tune really well, from the first set through the rest of their lifespan.
(EDIT 2 - Some amount of the pre-stretch achieved is coming out of the slack in the tuner posts and the string wrap around the ball-end at the bridge. With a Floyd (locking nut and bridge saddles), there's nothing but pure string between the lock points. It still stretches when brand new, but not as much.)