The first train from Paris arrives at St. Pancras after 9 am (so that's pretty much mid morning). Then I will have to find my way to the HoHo bus from there, so by that time I am on the bus, more time will have elapsed.
Looking at the Eurostar schedule back to Paris, the 7 pm train has sold out, so that only leaves the 6 and the 10 pm trains. However, because I am a senior, I might be so tired to stay until the 10 pm train so I will probably want to take the 6 pm train back whicih means I have to find my way to St. Pancras from any of the HoHo routes.
I am now thinking, is it even worth it going or should I just wait until I have more time to spend in London?
I do not plan on getting out of the bus, but just to see the sights and take pictures from the bus, (but maybe go on The Eye, that's about it.)