When is it the right time to ask someone to marry you?

So I'm in an amazing relationship with an Army man! It has been 9 months and we both agree that we have an awesome connection and have talked about marriage (he brought it up the 3rd month of dating me) Anyway, he's deployed and I miss him terribly. But, I thought, when is it best to propose? 6 months and up? I know it hasn't been a year and we want to get a place but I honestly think about it a lot lol

Thanks!