First, you've to convert times into second, sum them and than convert back. Something like

h0 = "00:00:00"
h1="04:00:00"
h2="03:30:00"
sec1 = CTOT(h1) - CTOT(h0)
sec2 = CTOT(h2) - CTOT(h0)
SecSum = sec1 + sec2
hSum = PADL(INT(SecSum/3600), 2, "0") + ":" + ;
		PADL(INT((SecSum%3600)/60),2, "0") + ":" + ;
		PADL(SecSum % 60,2, "0") 
? hSum

>I only want to add two variables with that format (add hours)
>h1="04:00:00"
>h2="03:30:00"
>or this
>h1="0400"
>h2="0330"
>As I should make it?