Can't think of a real simple way, but this should do it:
One method might be to convert the fields to their seconds equivalent, and then just use the standard seconds to time format (I have a FAQ on this in one of the Crystal forums).
Here's another thought too:
Details formula to add each element up of a time type:
whileprintingrecords;
numbervar hours := hours+val(mid("00:15:18",1,2));
numbervar mins := hours+val(mid("00:50:18",4,2));
numbervar secs := hours+val(mid("02:11:18",7,2));
To display it:
whileprintingrecords;
numbervar hours ;
numbervar mins ;
numbervar secs ;
totsec := remainder(secs,60)
totmins := remainder(mins/60)+truncate(secs/60)
tothours := hours+truncate(secs/60)
totext(tothours,"",0)+":"+totext(totmins,"",0)+":"+totext(totsecs,"",0)+":"+
-k