I'd guess, based on geography, that the Vulcan's display at Headcorn will be in between its slot at the Herne Bay display and that at Eastbourne, or vice versa.
It's due at Eastbourne at 14:29 local, according to here:
Daily Flying Schedule
Unfortunately, the Herne Bay display timings are in their souvenir programme which will cost you a fiver to download:
Amy Johnson Memorial Air Show | Sat 15th August 2015 - Herne Bay | The Riviera of Kent
So I guess it depends how keen you are to see it ...