I'm having trouble calculating the correct time laps.

start_time = DateTime.Now
(program code)
Dim processing_time As TimeSpan = DateTime.Now - start_time
msgbox(processing_time.Minutes)

start - 3/13/2013 7:49:30 PM
end - 3/13/2013 10:57:10 PM

My result was 7 mins. It seems like my code is not subtracting the hours. How do I correct this?