I have a large list of times. There are in fact how long a call lasts.
Unfortunatly they are in the wron format. The format is 00:00:00 hours,
minutes, seconds.

I have changed their format to time, but when I sum them I get 00:00:00 as
the result.

But if I double click on a cell then click off it again the formatting
changes. The entries go from being left justified to right and the sum
function now works. In the undo drop down it say it wants to undo Typing
'0:01:03' in N4 for example.

How can I do this automaticaly because I have about 12,000 entries?