I don't think the problem here is that convoi's can have their own waiting times, but that copying a convoi doesn't copy the template convoi's individual waiting time. That shouldn't be much of a problem. If the player didn't want to make a new convoi with a waiting time different from the line's default, why then did the player copy the convoi which does and expect that to work? (Apart from the fact that it for whatever reason works that way now, but how many have discovered that?)