They all wintersow just fine. It doesn't matter when you start them, because they'll germinate when they're ready, and aren't damaged by cold winters. Just make sure the medium isn't wet enough to rot them, particularly in warmer temps.

Melica will probably reach nearly a foot high in the first year, and depending on variety, will make full height in the second year.

Panicum and Sorghastrum will take 3 years to reach mature height.

I've never had any critter damage with any of them, but apart from squirrels and raccoons, I don't have any critter problems here. From everything I've read, though, bunnies won't bother them.

I winter-sowed several native prairie grasses 2 years ago, including Sorghastrum nutans. I just checked my records, and they were all sown on April 12 and most sprouted around April 24th. They are warm season grasses, so they will sprout when the weather is warm enough. I sowed them in little clumps and then divided them once or twice when planted out. They didn't get very big the first year, but grew much bigger and bloomed a little this past summer.

The resident rabbit out back didn't bother the grasses, but it did demolish the native clover seedlings I planted. 8-/