It really depends on the particular autoflower....I've had some finish in 65 days from seed (la diva from delicious seeds)....ran it 24 hours under a 400w mh/hps and it did about 31g dry..........Then again, doing 2 others right now (blue diesel from short stuff, Super Cali Haze from Short Stuff)...and getting different results....B.D. is about to finish (90 days from seed approx)...where as my Cali Haze is nearing 5 months and it just now starting to show flowering once I moved it into 12/12....proving that sometimes the Auto genetics aren't as strong.....Autos I'm not a huge fan of....Cant clone em without damn near killing it in stress, don't yield much and are very unpredictable, both sexing (even fem) and with flowering times.....
just my 2cents