The last few times I've gotten blue bottles for mine, they started flying within a day. I put the pupaes in a ventilated glass jar so that way the glass would keep in heat from the 20 watt bulb I have aimed at a few of my jars. Kept it around 80 degrees in the jar. They were flying within 24 hours of hatching. Pupaes can be kept in the fridge (as long as it isn't too cold) to slow them down from hatching. Keep in mind though, that the longer you keep them, the lower your hatch rate percentage becomes over time. They can be stored for up to 3 weeks before their hatch rates start to drastically fall. Once hatched, they can survive up to a month with food and water.
I'm switching to house flies on my next order though. Reason: only difference between the blue bottle fly and the house fly really is a little bit of color, and a blue bottle is slightly bigger, but not by much. I can buy
100 blue bottle fly pupae for $3.95, while I can get
500 house fly pupae for $2.95. So for a dollar less, I can get 400 more flies. Granted, after 2-3 weeks, the hatch rates on blue bottle flies will be a little better than the hatch rates on house flies, as the blue bottles are a bit hardier. BUT..... I will have
400 MORE house flies, and even if 200 of those die off, I'm still 200 in the positive over B.B. flies. I'm going to feed just a few more of the house flies to my cham than I did with the B.B. flies because of super slight size difference, but with an extra 400 flies to play with, I can more at a time and still have enough flies to last me a while.
My plan to prevent die-offs is to hatch 150 or so every 5 days, and then always provide them with food and water. This way, I can get them all hatched before their hatch rates start to drop, and then they will stay alive for 3-4 weeks after that, giving me plenty of time gutload them and feed them off.
I've looked around lots on my many feeder research sprees, and one of the site sponsors here, Mantisplace.com, has the best prices on flies that I've seen. They are only a state away from me as well so that works out really good and saves me from having to pay for priority shipping because they get here in a day or two anyways with standard shipping. I might just have a heat or cold pack once in a while which is super cheap.
Another good place is Mantidpets.com which is based in Oklahoma. This site might be good for people that live a little closer that way than buying from Mantisplace, which is based in Ohio. A tad bit more expensive at Mantidpets but it's all about what works best for you. I used to get my flies there a couple times before I found out that Mantisplace.com was closer and less expensive. Now I'm never turning back.