Read the second part of my first posting, ie:

" ...
If this is the case, then in a blank column enter the formula:

=A1/60, assuming your times are in column A, and format as [m]:ss. Copy

this down.

You can fix the values using <copy with Edit | Paste Special | Values
| OK, and you can also paste the fixed values to over-write the
original values. Hopefully, your SUM and AVERAGE formulae will work
after this.

Hope this helps.
...."

And I hope this re-posting helps.

Pete