if so you will have all your numbers assigned at 36 hour mark....
If NOT, when you check in at any time after the 24 hour mark, the other two will be assigned numbers at that point, but the number your husband "gets" will have been assigned at 36 hour mark
I booked my September trip on the first day fares were released and got $79 each way. If I remember correctly even later that day fares jumped up quite a bit. I have been checking a few times a week and haven't seen any cheaper fares on SW (although they do jump around a bit). I rarely see Dings from Midway to Orlando so for me it didn't make sense for me to wait.
My advice would be to book as soon as possible if the fares are good.