Mine have started to hatch only now. I found that you don't store them in the fridge. I have mine stored on a table at room temp. Today, I got 15 of them and now put them into the fridge. I will take them out again tonight and leave them sitting in room temp overnight. I should have more tomorrow morning.
It has taken almost a week for them to start hatching at room temp.
Jessb, the maggot builds a casing around itself. When the casing goes a really dark or black colour, the fly comes out. The piccys are not the best, but I captured one hatching and what they look like in the container. One thing but, god they stink.