if it's a typical auto, i figure i have about 4-5 weeks of vege growth. Breeder info may help on this guesstimate too. So, i try to let the termina bud grow vertically when i think it will catch up to the others by the end of vege growth...
so, it's a bit of a guess... familiarity with a strain will go a long way. last time i grew an auto, i shot for 6-7 shoots and the timing worked well for that. I think i could ge tmore out of an autoflower now, though... so, environment and numerous other variables make this dangerous to suggest to someone.
Take anything said here as a grain of salt. React to plant as best you can. The next time will be that much better if you take notice of what you do this time. take some notes, a picture etc... diaries help.