Formatting Cells for Time

I am extracting data from an outside database that contains minimum and maximun times for file processing. The extracted colum of time (for example) looks like this:
+00:02:07.35000. I initially highlighted the column, and did Format Cells, Custom, and chose h:mm:ss. I then did a Find +00, Replace All to remove the +00. I ended up with
12:07:35 on the bar, and appears as 07:35 AM in the cell. I'm then able to get an average time for the entire column using a =sum(a1:b3)/2 formula.

This worked one day for the entire column, but when attempting to perform the same steps on another extract of the same data, just different month, I'm unable to format the cells, and the formula calculates to 0. The cells show as being Custom. I don't know if I changed an Excel setting in error, but this is an issue.

thanks for any input....