From: Leeuwarden, Netherlands
My experience with the Dutch scenario, having played it a few times as Germany (and now as the Dutch), is that because of the tight time limit it doesn't pay to conquer or destroy them all.
Keyword is speed here. Therefor push the opposing units away, race past them with your fast units, and keep the encircled units under control with *just enough* units of your own to hold them in check. I'm not familiar enough with the game to say how long it actually takes in gametime for the enemy units to wither away, but at least more than one. A turn of two, three I'd say, maybe four?
I tried to destroy all of the Dutch units, but that took too long, giving me a defeat as Germany a few times.
I haven't tried this in Poland yet though...