I'm in a pickle so I come seeking the experts!

I have a range of data that contains cells that report time in hours mins and seconds. If the amount of time is in seconds only, it's reporting as :00 and causing me problems when I lookup to it...specificially it returns nothing. My formulas use iserror so prevent errors showing up.

What I need is a script or macro that searches the range (a1:z20) and finds all cells there the leftmost char is a colon and replaces it with 0:

Any help on this would be greatly appreciated. (I do 30 pages of this a day and need a faster way to go through them)