Care the port road becomes absolutely gridlocked from 8 am to early afternoon.
The castle is on the other side of town and up a steep hill. It may require a taxi up there, but could walk back.
It opens 10 am.
I have seen when disembarking the porters taking cruise luggage at 9 am but I do not recommend it, those turning up, we’re turned away. Best to arrive after 10.30 am.
Many cruisers book an incorporated tour from London to port with a stop at the castle where they keep your luggage
Such as.
https://www.internationalfriends.co...hrow-to-dover-with-optional-dover-castle.html
I do not recommend stays in Dover, quite seedy there, but if you wish to the Best Western Dover Marina is convenient and on a good day you could walk to the terminal if your fit.
Canterbury is a far better alternative