I made a diary and pollinated an auto with its sister and got a good amount of viable seeds out of it. One mistake I made was not starting one plant a little bit later when it would be at the height of flowering potential. However if you all ready have the pollen collected and its stored well, I would give it a few weeks into flower when its producing lots of sites. My problem was I was producing pollen and pollinating plants at the same time.
Ezzjaybruh also does a lot of breeding and their answer is right on the money.
One last note on autos, they can easily go past 15weeks but the buds just get crazy amber and the plant does not grow at all. It's useful for maturing seeds. give them at min 4weeks or best results let the plant go on as long as it can.
Good Luck!
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