Flowering stage for noobs

There is no such thing as too long. Different strains and genetics will have different flowering and finishing times, for example an indica can finish in 6-9 weeks but a sativa can go 9-20 weeks

15 weeks flower is usually enough for any plant to self pollinate but sativas can go even longer probably about 20 weeks you get some of the highest yields growing this way but you haveto be on top on the signs else you could end up with a bunch of seeds. 10 weeks is usually enough for any indica strain about 12 or more for sativas :)

Look up your strain your growing on Google you'll find your answer every strain is different so times will vary