From the CLI you can set the ARP cache timeout by issueing the command set system setting arp-cache-timeout <value> with the minimum being 60 seconds and the maximum being 65535 seconds. This of course is system wide and can't be adjusted for just one interface.
If you could script something to trigger when your F5 device logs a failover event, in a Slunk for example, you could utilize the API to clear the arp on the interface by issuing the clear arp <interface> command via the API. /api/?type=op&cmd=<clear><arp>interface</arp</clear>
We have the same setup (using default arp cache timeouts) and we do not see this issue. everything fails over smoothly
p.s. to see your current arp cache timeout use: show arp all
it appears there is a bug with show system setting arp-cache-timeout (valid command seen here: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-new-features/networking-features/arp-cache-timeo...) because when I try that one I get an error but show arp all gives me the info
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