Calc Minutes And Seconds Difference

Spreadsheet tracks race times for cross country races and needs to be able to
calculate improvement time in mm:ss (or zero if less than previous race).

Also,it would be nice to be able to enter times without using colons or have
to reference the field as h:mm:ss. The race result will always be mm:ss and
the last two digits will always be seconds, the result will never be more
than 60 minutes so hours are a real bother.

A1 (8:52, m:ss) - A2 (8:40, mm:ss) should = 0.12 (12 seconds)

Presently I am using the following: =TEXT(A2-A1,"h:mm:ss"), I only want to
display m:ss, hours are meanlingless