The tide turning time is right. In fact, as the ship arrived in what used to be called "The Pool of London'' I checked the tide tables and wondered where the barge might have moored because it wouldn't have been able to go any further upriver. London Bridge (the one still here, not the one now in the US) is the next bridge upstream and it's too low for the barge to have passed. The most logical mooring nearby would in St Katherine's dock but that's downstream from Tower Bridge. Which is why I found myself speculating about the need to pass Tower Bridge at rush hour.
(As we were messing around on bikes on cycleways and side roads, it didn't involve us, but now that we all seem to have to drive bigger and bigger cars in less road space, we saw a lot of stationary traffic. I haven't asked
@PeteXXX about how much he was held up on Tower Bridge itself but it was close to 7pm and virtually gridlocked when I last saw him.)