Now, I am really in trouble because I want them the be in mm:ss not hh:mm:ss
i.e. the first number should be 0:20:12. Can you help with this? or another
forum is needed here.

"Pete" wrote:

Yes, if you do Format | Cells | Number (tab) then it shows Time with
13:30 - this means hours and minutes. Click on 13:30:55 (two down on
the list) and you should see your first value change to 20:12:00, in
which case it is formatted as I suggested and you can follow my
suggestions to rectify it.

Pete