I have 5 indoor Durban Poison plants, 10 weeks post-germination, 3 wk seedlings transplanted and they have been vegetative for 7 wks. The seeds were not feminized and I had hoped to get any boys out based on pre-flowers before flipping to flowering. My feeling is to complete 2 more weeks of veg and if I still can’t determine sex, flip to flowering. Advice anyone? Thanks.
Flip them. Boys will show before the girls so just keep a close eye on them for the first few weeks
Agree with @Daddy the males will normally show first. I came out with 5 males and 4 females from my DP outdoor grow.
You guys are right on the money 
Flip to 12/12 and within 2-3 weeks you’ll be able to tell what sex they are. Remove the males carefully once you’re sure and you’ll be fine. Best of luck on the crap shoot!
Thank you! Here on out, only feminized seed 
Thank you! Here on out, feminized seed only
It really is the best way. Bag seeds can be up to 70% boys 