Kate Filmore: This guy sure moves quickly, he's just gone.
Jerry Whitehall: Sixty thousand, six hundred and fifty-nine rooms? Christ.
Kate Filmore: This place must be huge.
Mrs. Paley: Oh, yes, yes. In a hypercube, there could be 60 million rooms.
Jerry Whitehall: Each one of these rooms has six of these doors and portals, but no matter how many different doors and portals I go through I always end up in the same three rooms.
Kate Filmore: Who are you?
Simon Grady: Yeah, it's me. Good old Simon. Do you remember this, do you? Well, I've waited a long time for payback.
Kate Filmore: But, that was just seconds ago.
Simon Grady: Don't be so stupid Kate. You know time works differently in this place.
Kate Filmore: Are you okay? Did you hit your head?
Max Reisler: Yeah, I slipped. It's a wall - it wiggled.
Chosen answer: I'm inclined to think it was longer than a month because of the lack of proper needed care for such an injury would prolong the healing process. But he only had a handful of souvenirs on him, which means he probably stopped collecting after a while. I concur with your cannibalism theory, there's no other way he would have survived. However that doesn't explain what he could have done for water. This theory of Simon spending possibly months in the cube also brings up the question: If the cube breaks down at 6:06:59, then how is it possible to live in there for months? Well, as we saw, certain rooms have slower and faster rates of time. So, he could have spent all that time in a room with a slow time rate waiting for people to wander into it and feed off of them.