you can do one of two things,
You can either insert a line into a database witha time and date stamp and select count * from XXX where Datetime.hours < 24 or something like that.
You could open up an file you keep on the server, keep 1 digit in there and add one each time a add is displayed and pull from that number when the label shows the number.
I would suggest SQL server route if you have that ability.
Let me know if you need help.
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