About 25mins in - when Lister cuts Cat's ponytail off you can clearly see the timer on Lister's groin bomb box has clicked down to 00.00. This is clearly seen throughout this scene.
Later in the lift it says 80.00, and then they get out of the lift and it's suddenly 72.00.
When they are talking about evolving the Doctor back to her human form the timer is at 00.00 again.
It finally counts down again and is defused at 00.02.
Rimmer walks through the wall by switching his hologram mode from "hard light" (solid) to "soft light" (projected image). However, it has been established that his image is projected by a "light bee" device, which is always solid and should not have been able to get through the wall.