well from my expe3rience with p.paradoxa, they can go for long periods refusing to eat, crickets or not. but its much likely theyll want to eat if its something that isnt crickets (flies and moths etc). ive never had one die of starvation becauses it refuses to eat crickets because ive offered them other things, so i dont know how far theyre willing to pursue their pickyness. also, i may be wrong with this and many would disagree and say its down to the crickets diet, but im just not very trusting of crickets at all. some might say that nutrionally they arent so good for the mantis. so even if it did "cave in" and eat crickets, i dont think itd be the best for the mantis, from a nutritional standing. but then some say crickets are fine nutrionaly, its just what you feed them that matters. so umm yeh i guess its up to you, but i would say avoid them if you can.
im not too sure how long waxmoths take to hatch from the pupa, i think its one or two weeks, im probably wrong, and it depend son temperature too. the most conveninet method of using flying insects as food is to buy lots of maggots from a fishing tackle/bait shops, keep them in the fridge or something. every few days, take a few out and keep them at room temperature. you wont get anything for a week or two but if you keep doing this every few days, eventually the first maggots you took out will have turned into flies, then you get new flies hatching every couple of days. some people find this a pain but i think its pretty useful and eays once you get into that routine. but yeh there are better threads on flies elsewhere. sorry i cant help much.
EDIT: like 13ollox suggests above, this method works well for waxworm/moths too.