Originally Posted by stut

It's the day, rather than the 24 hours, although the 'day' extends to 4am (not that this really helps you...)

However, given the journeys you're doing, it sounds like a PAYG Oyster card will be better, as you're only going to be doing one or two in a day (and buses may be a better bet than the Tube for some).

The only day for which I'd really recommend a travelcard over an Oyster card is when you're going to the Tower of London, and if there's more than one of you visiting. If so, then a National Rail (not Tube - although it is valid on the Tube) Travelcard will get you a very valuable 2-for-1 on entry.