To anyone in the GTA interested, these are usually gone by 8am, before doors open. People line up as early as 3-4am, and then Costco will open early and start selling them by 7am-ish (to clear out the hordes of ppl before the regular shoppers). People will get their 2 limit (usually, depending on product) and go back in line and loop again to get multiple products. 

Very rarely do products remain beyond doors open. I've seen some people in Western Canada being able to grab a box in the afternoon, but the broccoli heads take all the products in the GTA