Players and coaches constantly are with their teams, allowing for testing to happen on a regular basis within the confines of a fairly controlled environment. Officials, on the other hand, will go about their normal lives during the week before showing up for games.
Per a source with knowledge of the situation, the officials will be tested during the week in their home market, and again in the city where the game they are officiating will be played.
Given the 24-hour turnaround for testing, it will require the officials to arrive at the site of the game at least one day before kickoff -- and the league will need to be prepared for the possibility that one or more officials will test positive at a given game site. As previously explained, the league is prepared to proceed with as few as five officials on the field per game.