I'm a little late here, but don't forget to incubate them before putting them in the fridge so that they can develop to the diapause stage first. Or, you can just break the diapause by dunking the eggs in mineral oil lol. Also, Melanoplus femurrubrum are perfectly legal to ship, just FYI. Good luck!
Edit: I'm pretty sure the shortening of the diapause experiment was done over many generations, so 3 weeks is way too short in my opinion, but let me know how it goes if you decide to follow through with it. I've only been breeding non-diapausing species for the past few years, so I'm definitely interested in your results. I only recently picked up 3 new species of large diapausing grasshoppers to work with.