Doesn't Roy open the cafe on weekends? Saturdays at least? It always seems to be open. And wouldn't they hear Norris hollering from down below them or hear the lavvy flush over the weekend?
Even if the cafe is closed, Roy and Hayley still use the staircase right next to the lavvy to go up and down and out of the flat through the cafe all the time. As far as I know, there is no other external door to the flat other than through the business premises. Surely Norris would hear someone coming and make noise.
I might believe an overnight in the loo, but not a whole weekend. Sorry. Can't buy this one.