I was referred to this question from this one :http://chimigan.com/27212/
So I explain same thing here:
Every hour on the hour means: Something happens frequently with intervals of one hour in between; but it also stress that it starts exactly at the minute 0 of each hour.
I just googled it and this popped out:
The expression "every hour on the hour" is more precise than "every hour".
The train for Leicester leaves every hour at 15 minutes past the hour. It leaves at 0:15, 1:15, etc.
The clock strikes every hour on the hour. It strikes at 0:00, 1:00, 2:00, etc.
from :http://forum.wordreference.com/showthread.php?t=1833164
So the best equivalent Persian I came up with is: