Nope... Remove the pikemen standing on the swamp – the speed will increase even more! And this happens throughout the day. That is, you can remove the penalties during the day by removing the units that slow down movement on rough terrain from your army... And that's why the speed increases...
But if, in addition to the pikemen, there are other warrior units in the army that have a penalty for walking on the swamp, then this will not change anything.
I'm not arguing, the penalties change, which is why the pikemen are dismissed.