It would be much more readable and efficient if you just did it like this:
Dim timeTook As Stopwatch = Stopwatch.StartNew
'Some time-consuming tasks
timeTook.Stop()
Label3.Text = "Time took: " & Math.Floor(timeTook.Elapsed.TotalMinutes).ToString() & " Minutes and " & timeTook.Elapsed.Seconds.ToString() & " Seconds"
Or better yet:
Label3.Text = "Time took: " & timeTook.Elapsed.ToString()
The Elapsed
property already has all the information you need, so it's silly, and more error prone, for you to recalculate it all yourself.