Help converting times to numbers.

0:20:52 20:52 6:43

So I copied some marathon times data from their online websites. When I copied them to excel it seems they are in different formats. Like if I change them all to #:##:## then looking above the numbers would appear like 0:20:52 or 0:00:20.52. (I have attached an excel file). I need each of the columns (C, D, E in the Excel file) converted to seconds. So the above will yield...

1252 1252 403

into the O, P, and Q columns in my example sheet. In the real sheet I'll be converting 1000s of times but can simply drag the function down.

Can you help me? And THANKS ahead of time!

Dr. Gannon