Now, I think you meant that for every minute outside equated to one hour inside. And if that is what you meant to say then it is more around the figure of 420 days or 14 months; but that really doesn't matter, it's your story after all, you get to write it as you see fit.
As for the story itself, I just started reading it and I like the direction you're heading in but I feel you're rushing the story a bit, maybe longer chapters or something, I don't know but either way, again it's your story and I do rather enjoy it and I will continue to read it. Hope you don't consider this as an act of Flaming or whatever but more in the lines of constructive criticism.