When I used a bathroom as a temporary darkroom I found that getting out the enlarger and setting it up took the most time. I solved that problem by replacing the shower head with a pipe cap and I kept the enlarger setup in the shower. This was possible because this bathroom was just off the family room and had a shower in case of guests (I assume). Everything was kept in the shower area so that it could be set up quickly on the sink (set into a 5 foot long counter).
The next time user was blocking out the light. It took several tries, but with the right choice of weatherstripping and making sure no one turned the light on in the adjoining hallway, this portion of the setup was eliminated.