The guest user is able to select the time required, up to the maximum.  The person doing the sponsoring does not have control.   https://documentation.meraki.com/MR/Encryption_and_Authentication/Sponsored_Guest   "The session time can be set to: automatically grant the access duration (30 minutes to 6 weeks) specified by the “Maximum sponsorship duration” during the splash page registration allow users to request access for a session duration that is limited by the “Maximum sponsorship duration” specified by the Meraki Administrator" ... View more