Here are my thoughts:
Changing of the Guard,
-->The change itself is about a 30-45 minute thing with a lot of wait time in the middle. You'll want to get there early to get a spot but I'm not sure how much earlier in November. This website gives you down to the minute timings.
https://www.householddivision.org.uk/index.php?action=changing-the-guard-calendar
Westminster Abbey,
--> probably at least 90-120 minutes. You can download the audio guide ahead of time to your smartphone instead of having to use the free ones there. Take your earbuds with you. I saw something recently that Stephen Hawking's ashes were interred in June. When I was there in May the docent I was talking to said he was to be interred right next to Isaac Newton, so look for that new stone on the floor.
War Rooms,
-->I'd say 2 hours if you don't spend much time in the Churchill exhibit rooms or 3 hours if you do
V&A Museum,/British Museum,
-->Agree with a poster upthread. As much time as you want, possibly a lifetime between these 2 museums. I'd go with the approach to look online ahead of time to see what galleries would be of interest and then do some precision touring here. I've made the error of spending 5 hours at the British Museum and just overwhelmed myself. I'd set a limit for 2-3 hours each. It's also easy to get turned around in these museums as not everything seems to connect up.
National Gallery,
-->Again, check ahead and decide what you want to see. The docents here are excellent at being able to tell you how to get from say the Impressionists galleries to Rembrandt, lol.
St. Paul's Cathedral,
-->90 minutes minimum
Tower of London,
-->I'm the one (or one of the ones) that said 2 hours was too little for Tower of London. I'd day 3-4 hours including time for a break for food or a snack. It's very big on the inside which is a slightly dumb statement but what I mean is there is lots of walking. It will depend on the weather as to how much outside stuff you'd like to do as well.
Queen's Gallery,
--> Are you sure the Queen's Gallery will have an exhibit on when you are there? I'm not sure it's open unless they have a special exhibition but I'm not 100% sure of this. When I stopped in there in May (gift shop, hahhaa) they were between exhibits and the gallery was closed.
https://www.royalcollection.org.uk/visit/the-queens-gallery-buckingham-palace
Royal Mews
-->Maybe an hour at most.