Took haldol (haloperidol) cogentin. How long do side effects last?

Up tp 24 hours or so. The side effects of Haldol (haloperidol) should normally take about 24 hours, but some such as akathesia may take a couple of days. As for cogentin, if you took only one dose, the effects should mostly abate after 24 hours, definitely in 36 hours.