How long to wait until hiring a GM?"

With several teams looking to get new head coaches next year, does it make sense to wait until the end of the season to hire a GM and potentially be behind the curve when it comes to potential head coach candidates? One name that pops up alot is Louis Reddick who isn't part of any NFL organization and can be hired off the street. Unless Cal McNair wants to wait until the end of the season to try and interview Caserio from New England (again) there is no reason to not start interviewing the people who are available