I'm only on my first grow so I'm not speaking from much experience but I have six 3 gallon canvas pots with the same strain growing in Coco/Perlite, this strain (Northern Lights x Big Buds Auto from Weedseedsexpress.com) was listed as 11-13 weeks to finish and it iis the end of week 14 going on week 15 from today, most will probably finish up this week but some can be left for another week.
I had a 7th plant that started in a small 1/2 L pot and later transplanted in to a 1 gallon (approx) because it was rootbound.
Plant No. 7 I was chopping and smoking from already at week 10 but some of the bigger pots still have a week or even two to go and they even look at 2 or 3 different stages in the same pots, biggest plant of the six will probably yield 3 times as much as the one I chopped down yesterday (268g of proper trimmed dense buds *wet weight* now drying and another 80-90 gram of sugar coated wet trim for the freezer.
I'm sure pot size plays a part but so does Topping, LST, Defoliation and Trimming, 2-3 weeks in finishing difference and big difference in yield is just something we have to accept in Autos I think, some strains more than others probably.