This article applies to all the versions of Aruba OS
The PMKID is cached for 8hrs by default. However this is configurable from the 802.1X Authentication Profile.
(Aruba) (config) #show aaa authentication dot1x default | include PMKSA
Time interval after which the PMKSA will be deleted 8 hr(s)
(Aruba) (config) #aaa authentication dot1x default
(Aruba) (802.1X Authentication Profile "default") #timer keycache-tmout ?
<kc-tmout> Time interval in Hours. Range: 1-2000. Default: 8 hrs.