BitVoteTimer

The amount of vote-time you have ready to spend is

 Available Time = Current Time - Registered Time - Spent Time

However, it may just be calculated as.

 Available Time = Current Time - Moving Time

Where Moving Time is moved forward by the time you vote whenever you vote, and cannot be moved beyond the current time.

Additionally, there may be a upper limit of available time. For instance one year. The reason is to not give 'waiters' too much power.