Just adding to the really old post since it still shows up in searches. What I have here might not have even worked in 2005. I'm using LabVIEW 2012 (Yes, I'd prefer to be using the newest version!).
 
You can use the Format into String VI with a relative time format specifier ("t" rather than "T"). The formatting rolls to the largest time unit in the specifier.
 
 
 
The formatted time indicator shows the elapsed time with the largest time unit set to days, hours, minutes, and seconds.
 
 
Note that the Elapsed Time control is just a numeric with the format set to relative time.

 
					
				
			
			
				
	David Grucza, CLD