We haven't heard many teams publicly acknowledge a deadline in which the NFL lockout needs to end before training camp can resume at its normally schedule time. The Minnesota Vikings, though, sent a letter to Minnesota State University, site of their training camp, informing them that they would let them know of camp plans by July 18.
If the NFL lockout lasts until that date, it's possible the Vikings will make plans to stay at home.
That would be roughly less than two weeks before most teams would usually start training camp. We can't say for certain whether other teams have similar schedules but a two-week notice sounds about right.
The best case scenario is the NFL owners and players reaching an agreement on a new CBA and ending the lockout before that point. That makes this question of training camp start dates a moot point.
But if the two sides can't reach an agreement, then the middle of July becomes a key date for most teams. About 15 teams still go on the road for training camp and those would be the teams that are affected the most because their camp schedule is dependent on the schedule of whoever is hosting it.
Most of those 15 teams head to smaller cities or colleges for camp and their presence brings a nice financial boost so folks want to know what the plan is.