I recall that there is an option for the setting of the splash page frequency, so quite possibly if the IP lease is long enough, a specific, previously authorised user does not have to re-authenticate if the DHCP lease is still valid.
I do recall a situation at a village pub where the guest network handed out long IP leases and the regulars would keep the same IP pretty well indefinitely. Which made for some interesting analysis, particularly when it came to unnoticed coincidences. The management were usually weeks ahead of the village gossips.