I don't know if heat stress can delay flowering or not, but I assume it would, my first grow they showed sex a lot sooner than these, first grow was in basement, this one in attic, we've had a heat wave the last couple weeks, before I got a bigger exhaust fan and and added intake fan, it was getting about 104-110 during the day with lights off, plants never got too "ugly" looking like they were in a bad way, but at about 6 weeks old, they're pretty puny looking, they haven't had but a couple inches of growth the last 2 or 3 weeks, and since I've gotten temps under control the last few days I've had more growth than in the last few weeks, so I figure no sign of sex has to be caused by heat stress, but I could be wrong, I'm far from expert at it