Hi,
I allow the air temps for my snakes (all of them, balls included) to drop down into the mid to high sixties at night, sometimes a few degrees lower. Their heat tapes are on night and day and range between 98F during the day to 80F on cool nights. The snakes go on and off the tapes during the night and make temperature selections based on their needs. They do this whether they have food in their systems or not. It is my opinion that most keepers keep their snakes a bit too warm. It is natural for these animals (all snakes) to get cooler at night, it is what they are programmed to do. When they are in good health with a functioning immune system, cool nights will not bother them at all. I have been keeping balls for 30 years and can count the RIs on one hand. As long as their cool nights are balanced with hot options during the day, problems don't normally occur.
I am a Frank Retes (pioneering king, python and monitor breeder) desciple when it comes to temperatures, I believe in giving them choices that are a little bit above and a little bit below what they need. They decide what they need and make the appropriate selection. It no longer surprises me to see a ball, carpet, diamond, green tree or Boelen's python sitting with a belly full of food on the cool side of the cage for a while at night. It also doesn't surprise me to see those same animals sitting under a lamp during the day at 105F for a while. They choose what they need, when they need it, and I just try to give them a range to pick from. As long as I see them making choices and not sticking on the cool or hot side all day (or night), I have no worries about them.
Sorry for the long winded response, but your temps seem fine to me. As long as they are not stressed and suffering from some immunosuppressing condition, they should be fine. Good luck.
Will