When you use the lasso tool to select multiple armies headed for the same destination, and you want to delay them so that they all reach their destination at the same time, there should be a button on the Delay Armies popup panel that, if the player presses it, would set the arrival time and individual stack delay time to match the stack that will take the longest to reach the destination.

For example, if three stacks are selected, one stack will take 3 hours, one will take 4, and one will take 6, if the button were pressed, it would delay Stack 1 for 3 hours and Stack 2 for 4 hours so that they will all arrive at the same time, and that there is no unnecessary surplus delaying.