IF they all decide to use the same spot to pee, it can smell like ammonia as it'll never dry up. If you have them trained to use a box with hay in it, just change it daily or every other day. Maybe try training them to use an Aspen bedding-filled litter box instead as that will mask some of the scent. To train them, rearrange their home and put some soiled hay in with the bedding. Every time after holding one (hold for 5 minutes or longer) put them right into the bedding box. They should go.
FWIW, I have a larger cage/pen than you and use Aspen bedding, and usually within 5~ days it can become noticeable, but it's mainly because several of them like to use the exact same spot to go in, so it either needs removed or the bedding needs shuffled so it'll air dry. If it's humid in your place, it might be worse. Also, since you are using a small alcove (cool idea) or hallway, there probably isn't much cross airflow, so it can get stagnate.