I honestly dont know, it depends a lot on the weather, if you have a cold snap, frost will kill off the eggs, if it is very hot and dry that too kills them off. They do best in damp warm conditions. With horses which is what I base the pigs on, about 6 weeks. Of course it depends a lot on if you can leave them off that paddock for 6 weeks. Otherwise just a couple of days but poo pick the paddock. The act of worming them is the most important bit. If any go for slaughter worm 6 weeks before slaughter date. Breeders I worm a couple of days before they are due. I worm everything ever 6 months regardless. Used to be 3 monthly until I was told that was too much, and I was damaging the pasture.
Dont worry, HM