Hi Aneel you can try this code..
NumberVar DVar := IIF((DATEDIFF("n",{PROBSUMMARYM1.OPEN_TIME},{PROBSUMMARYM1.CLOSE_TIME}) > 1440) ,(DATEDIFF("n",{PROBSUMMARYM1.OPEN_TIME},{PROBSUMMARYM1.CLOSE_TIME}) \ 1440) , 0);
Numbervar TempVar := (DATEDIFF("n",{PROBSUMMARYM1.OPEN_TIME},{PROBSUMMARYM1.CLOSE_TIME}) mod 1440);
NumberVar HVar := IIF(TempVar > 0 ,(TempVar \ 60) , 0);
Numbervar TempVar1 := (TempVar mod 60);
NumberVar MVar := IIF(TempVar1 > 0 ,((TempVar1 * 60) \ 60) , 0);
StringVar TimeTaken := TOTEXT(DVar,00) + ":Days " + TOTEXT(HVar,00) + ":Hours " + TOTEXT(MVar,00) + ":Minutes";
TimeTaken;