maybe get a new wireless AP?
this does sound to me like the delay is DHCP related so opperating in dumb AP mode may not help.
Be worth a try though?
Turn off DNS, DHCP etc on your linksys. plug a cable from LAN in the VF Modem into the LAN on Linksys modem.
Connect to wireless of Linksys. This will effectively put it into a dumb AP mode, allowing you to connect over it's wifi but have all routing handled by the Vodafone router.