What period of time do you wait after using a pour on dewormer before moving to a new pasture...??? Seems like I remember a period of 3-4 days, but...???
If you are concerned about shedding eggs and contaminating new pasture that has not previously been exposed, I would give the pour on a few days to disperse through their system, kill worms and clear out the egg load in the GI system. Depending on the parasiticide, they work fast.