The old man..?
In the beginning of the movie, Pete tries to convince Ray and Toby he went into the future. When they're back in the gents, the old man comes in and leaves again because of what he sees.
What time did he go?
And another thing, the old man jumps up again halfway the movie and leaves because of Pete who's holding a knife. So... The old man couldn't have gone into the toilets where he didn't see them doing their "Science experiment" so they caused a paradox, right?
Or om I wrong?