Flush 2 weeks before you think your going to harvest them. Usually at the 6-7 weeks mark depending on strain....thats considering you know the strain ha. But like when I grow bag seed I usually tend to flush between the 7-8 weeks mark. My bagseed always seems to take longer to flower though, like 10 weeks sometimes.
Edit: Yes your pots are too small for the plants. But really I made that same mistake on my first grow. 4 weeks into flowering I would say transplant them, some will tell you not too because you might stress them and hermie them. They say 1gal per 1 foot of growth....