Who can forget the “Lawrence Welk†trade of the century involving the Vikings, Cowboys and Hershel Walker in 1989. It’s called a “Lawrence Welk trade†because it involved “a ona and a twoa and a threeanda.†Those were the good old days in the NFL, when blockbuster trades occurred as often as Barry Sanders' unbelievable runs. The current problem with the NFL is that the trade deadline occurs too early in the season (after the sixth week), which effectively minimizes the chance of any substantial trades occurring, the current trade deadline also limits teams' abilities to get better during the season either for the short or long term. Five games into the NFL is just not enough time to make this determination, the NFL must take a serious look at this issue and ultimately decide to move the deadline back until mid-November or even Thanksgiving for the good of the league, the players, the teams and, most importantly, the fans. Source: The Washington Post
I'd say week 10. Gives plenty of time for any traded players to adapt and make an impact going into playoffs or a team to know if it might need to start planning for the future (ie: draft picks).
