1st Grow - Critical Cheese

I flipped the bloom switch on as advised by another grower but that first day was to much for the girls and they suffered heat stress and fell almost completely over. I shut the Veg off after that 1st day and left it off for 3 days or so. I turned the Veg switch back on after letting the girls recover and perk back up and they seem to be OK with the extra light now. I'm unsure when I should switch over to flower...i read about the plant stretching and gaining twice its height but a lot of small tent grows Ive seen don't seem to get that extra long stretch. I'm running only 1 - 450 watt LED unit, does anyone have any advice ? netting added to open up the middle of the plant and to get the canopy uniform.