Have you ever seen enemy's unit automatically inch forward without a stop?

Probably used the add target command

So in this case after I told the units to march to suceava, I selected the add target button and then Lvov. Then again selected add target and then Zamosc, and so on.

the point is automatically add target. People can manually add target to keep unit moving but not in their sleeping hour. I am not sure about the time zone of my enemy but this strange inch forward moving only happens in a fixed time window like someone is sleeping but machine is working.

Sometimes people add targets before they go to sleep. This is especially common when they expect light resistance from the enemy.

and this "add target" get renewed and repeat again and again for 12 hours?

I haven't found a limit as to how many add targets you can have. I've seen allies have a string of provinces targeted with add target which went a lot longer than 12 hours. So, it is a possible explanation. The only other way I can think of would be for the person to check in on the map and adjust movements. Or a combination of the two.

He could have delayed the attack as well.

By employing this tactic properly weather being online or offline

has no bearing on the stratagem.

Wayaya: an example the attacking player may be inching forward under

bombardment off rockets, and rockets inflict no damage to moving targets

or he may be inching forward under the pretext that the defending player

has rockets.

And there are quite a few stratagems why a player could employ

the tactic, but it is not uncommon and you will see quite alot of it

around rocket time.

This game mechanic is especially useful when you have artillery in the stack and use the aggressive fire control command in conjunction with it. When you do this, your stack will stop when it gets in range of an enemy, fire until it destroys the enemy, and then continue on its way. Of course, this always runs the risk of running into an alert enemy that can destroy your stack. But it can be very effective when you need to be offline for a while

it is my favorite thing to use on the game. if I will be gone for awhile I will get 40 units together and put them on a path for the time I will be gone and they will take the area.