It's a fair while since I watched it, but iirc the basic idea is that one of the guys took another machine back with him, and ended up 'duplicating' the characters, who then went slightly renegade, unknown to the other guy. The title (as in paint primer) refers to the original 24-hour period, before they went back to refine and improve everything, adding 'layers'.
Bearing in mind it was done on a tight indie budget, with no recourse to special effects, I reckon it was a damn good effort. As a result, the plot is fairly cerebral, so it needs a few viewings (imho).
...pretend here is reality, and not some expectant itch of july...