Dover to London by train and back to Dover cruise port

There are trains that take from 1-2 hours depending on time of day, etc. If you're only in town for a day on a cruise, I'd personally take a ship's excursion. Since you only have a few hours, the ship's excursions will take care of the transportation, getting you to/from various sites, will take care of ticket purchases for you (some perhaps skipping the line) and can help you maximize a very short day in port, plus will ensure you return to the ship on time.

If you've never been to London before, my favorites (thus far) are Tower of London and Westminster Abbey. Just those two things will take you at least 5 hours and that's pushing it.

There are two major options - the faster, high speed line which runs into St Pancras and the slower provincial line that runs into Charing Cross, Cannon Street or Victoria. Direct fast trains run once an hour and take about 1 hour 10 minutes, plus St Pancras probably isn’t anywhere near anything you would want to see, which would take you half an hour to reach by bus/tube/walking. Most of the faster trains involve a change at Ashford and take about 1.5 hours.

The slower trains are 2-2.5 hours, depending on if you have to change at Ashford. There are 5 trains an hour this morning between Dover and London between the hours of 9 and 10 am and 10 till 11 am. Last week, with the heat, there was a speed restriction on trains, which would have added about half an hour to all of these journeys, plus you would have to allow extra time in case delays or cancellations occur (not an infrequent event).

The cruise terminal is about 1.25 miles from Dover Priory station.

There are thousands of things to see in London so you need to work out what YOU want to see, not us, some of which maybe weather dependent, such as museums versus going on an organised walk. Allowing for 5 hours of travelling door to door as a minimum, do you really have 5-6 hours?

Canterbury is much closer and is easier to get to and from if there is a major problem with the trains.

Is your 5 to 6 hours including the transportation to and from London, or is it 5 or 6 hours once you are in London because you have allowed the time to get there and back to the ship?

I'm looking at your thread from June, just about a month ago - https://community.ricksteves.com/travel-forum/england/transportation-from-dover-to-london - but I'm not sure which...

Nigel. Ship arrives at 7:00 am but realistically won't be able to depart ship until 8:30. The ship sails at 7:00 pm which means we will have to give ourselves plenty of time to make it back to Dover. I realize we have very little time but hate to miss London completely if we are near. Thank you for taking time to help with this.