Is it good for that day or 24 hours?

IF it is good for 24 hours, then I think I can get away with buying 2 off peak Travel Cards for my 3 days.

I am landing in LHR on Weds afternoon.
So my plan is to buy a 1 day Travel Card (card #1) to get me to the Hilton on Park Lane.
Then use the card that night to check out London Bridge/Big Ben at night.

Then use the same card Thursday morning (since its less than 24 hours) to go to London Eye, walk back and go to Westminster Abbey, Big Ben and Buckingham Palace.

go to hotel for a conference call.

Take the tube to British Museum (card #2) Thursday afternoon

Friday morning - take the tube to Tower of London (using the same card, #2). walk back and visit the sites on the way.

Then Saturday morning, just purchase a 1 way ticket to LHR.

So, is this possible? (it all depends on whether its 24 hours)
Thanks