Although not considered full time employees, these guys have many hours a week dedicated to this effort.
The crew arives on Friday night at the game city. They spend that evening and Saturday reviewing tape of the 2 teams thay will see on Sunday, noting formations, shifts, special plays etc. and have a specific agenda up until game time. Then an extensive post game report is written and they are usually home late Sunday night. As one poster stated earlier they get reviewed by the NFL officiating office on each play and have phone meetings during the next couple of days.
So you are at the game city or traveling for 3 days, and 1-2 days of meetings, and physical training for the mid-week...I'd say these guys are pretty much full time.