Personally, I wouldn't ride right after floating. The vet (who recently did my horse's teeth) gave my horse a sedative before beginning that contained painkillers and some Bute afterwards. It's not that their teeth/gums will hurt afaterwards, but their jaws might be sore from being held open all that time. Also, it varies from horse to horse on how long it takes for the sedative to wear off. So I would ride before the floating or the day after, just to give the horse some time to recover.