I've had a look at this and want you to check if you're right. Dates and times are simply numbers. As I type this it's 27-04-2015 07:03. However, while that means something to you and me, it means nothing to Excel. To Excel, it's 42121.29375208.

The value in (for example) F10 appears to be 42:21:00, formatted as [h]:mm:ss (i.e. 15:20:00, formatted as hh].mm.ss). Are you 100% certain that it SHOULD be 42:21 mm:ss???