I understand that Excel always assumes the first unit of the time value is
hour. Example: If I enter 3:21, it means 3 hours and 21 minutes.

My problem is that I have lot of time data downloaded from another program
into Excel. The time is not displaced as I wish. Example: The information
3:21 should be 3 minutes and 21 seconds. Since the leading value of the hour
as 0 was not included, Excel assumes it's 3 hours and 21 minutes.

Can you think of any way that I can quickly change the data from hh:mm to
mm:ss?

Thanks in advance.

Anne