Your Voting Power replenishes at a rate of about 1% every 72 minutes.

From what I have read it takes about 24 hours for your Voting Power to replenish by about 20%.

How I to calculated it:
Firstly break down the hours into minutes.
24 hours x 60 minutes in an hour = 1440 minutes.
Then divide 1440 minutes by 20 to get the value of 1% (1440 divided 20 = 72)
Therefore you will have a replenishment of Voting Power at 1% every 72 minutes or every 1hr12min.

The advantage of knowing this is you can calculate how long it will take to hit your target percentage before you can vote again.

Hope this helps.