Hello Brian,
Under the Configure/WLANs page, and Edit your Guest Access WLAN, expand
the Advanced Options at the bottom of the box, and look for Grace Period. The
maximum value, 144000 corresponds to one week time period. Your visitor will
not need to enter their guest pass again, if they return within one week's time.
And the guest pass will be good for a year (365 days), as you configured.