Learn English – Word for the *other* day in a two-day cycle

My son's school operates on an A-day, B-day schedule, i.e. on a two-day cycle. Some classes meet every day, and some meet every other day, perhaps on A days, perhaps on B days. I need a word or a phrase to say the following:

Right now you have your science lab in Period 7 every other day. Let's ask if they'll let you do your foreign language in that slot on the other days.

I need a better word than other. Opposite comes to mind but I'm not sure if people will understand it. (School personnel are less sophisticated than you guys.)

Also, consider

But I'm not sure if they'll allow you to attend foreign language half time.

Is there something better than half time? Obviously, every other day would work, but in these conversations, I get really tired of saying "every other day" over and over again. Will people understand "half time"?

There is a thread about this where bidiurnal was suggested but that's too sophisticated for the school and for me.

If you need to rewrite my sentences slightly I am open to that.

Edit: I will experiment with DJClayworth's idea of replacing "every other" in Sentence 1. Here goes.

(DJ inspired) Right now you have your science lab in Period 7 on a half schedule. Let's ask if they'll let you do your foreign language in that slot on the other days.

Now I will try using the suggestion in the comment, alternate:

Version (a): Right now you have your science lab in Period 7 on alternate [or alternating] days. Let's ask if they'll let you do your foreign language in that slot on the other days.

Version (b) (playing further with DJ's idea): Right now you have your science lab half time in Period 7. Let's ask if they'll let you do your foreign language in that slot on the alternate days.