How long does it usually take for a plant to enter the flowering stage? I have heard once you put it onto 12/12 it will change stages, but how do i know when to put the lights on 12/12?
You can change the lights when the plant is about 20 inches tall.

And What is Auto flowering? Do you not change the light hours, and the plant will flower when ready?
I'm doing auto-flowering AK47's and I keep the light at 20/4 thru the whole grow, from begining to end.

And finally, how much of a difference do you think i would see, if I upgraded my lights. Now i have 1 120 watt, and a 3 26watt CFL's.
You will definetly see a difference if you increased your lights.
Read the sticky's on the basic growing forum, theres alot of info about how many lumens minumum per square feet, HPS, MH, and flouro's. etc.