bar chart measuring minutes (not clock time)

Hey guys,

I am trying to format a bar chart to measure the monthly call duration. Data in excel looks like this:

4:20
10:34
8:21

etc. It has to keep this minutes:seconds look for the chart data labels...not be converted to minutes in decimal form.

Which cell format will allow both the chart data labels and the Y axis labels to display that way? I've tried time formats and custom formats and nothing seems to work. They all either seem to want to convert it to an actual timestamp (11/1/10 4:20 AM) or change it to minutes in decimal form.

Thanks...