These have to be coming back as characters. Therefore they'll be ordered as characters.

20:1:1

comes before

20:2:5

No matter what the math, these are ordered by characters. If you have some rules, you could use charindex and substring to strip out the individual numbers and possibly find a way to order them, but the rules for reducing these to the lowest values would be complex.

Again, if you develop the rules that you need for ordering these, we might be able to help.