Critical Mass London: last friday of the month South Bank by National Theatre, 6.30pm

oh damn. just read "Take a cycle as often as you like per access period, leaving five minutes between each trip"

I don't think so, it doesn't count if you don't actually remove it from the dock AFAIK. Easiest way to check is to put your dongle into one of the terminals and check your account balance, or login to the Cycle Hire website and it'll show you.