I had been expecting for the past couple days that free agency would begin on July 25, after an exclusive 72 hour window to re-sign each teams' own free agents. It looks like the new estimate is to begin free agency on July 28. 

Three days might not sound like a big deal, but it makes it a lot more likely players could miss the start of training camp, which could start for the Green Bay Packers on Saturday, July 30. The players usually report a couple days early to take their physicals. That makes for a very tight schedule, if they can't sign any player not currently on the roster until July 28. 

The annual family night scrimmage is planned for Saturday, August 6 which might not involve any currently unsigned free agents depending on when they sign and report. If the Packers actually sign another unrestricted free agents from any other team, something they didn't do last year, then the team might not have enough time to properly evaluate them. It also would seem a real tough proposition for any undrafted rookie free agent to do anything other than show just enough promise to earn a spot on the practice squad.