Windows will look for the DC it has been using first. You turned that one off, so it needs to search for another to authenticate against. If you hae give the DC’s enough time to fully replicate, there would normally be a short delay in finding the new DC, but it should not be long. The extra time can be attributed, I believe, to missing information that had not yet been replicated. Turn up the original DC again, and you wil likely get the same delay until everything has been fully replicated.