I have some variables like these: a(1)=00:26:00 a(2)=744:32:00 a(3)=8040:33:00 I want to convert them to numbers, so I use the datenum command. The biggest number should be 8040:33:00, but look what happens. datenum(a([1 2 3])) ans = 1.0e+005 * 7.3487 7.3485 7.3486 But if I don´t calculate a(1): datenum(a([2 3],51)) ans = 1.0e+005 * 7.3490 7.3520 That´s the results that I want to get. I think that the problem is that a(2) and a(3) have more than 24hours but I haven´t found any way to solve this problem. Thanks.