I don't think that the deadline will be set until after the NHL playoffs because the U.S. coach is Ron Wilson, coach of San Jose, and the Sharks are probably going to the Stanley Cup finals. So they're probably giving him enough time so that he can actually focus on the World Cup after the playoffs are over.
Wait a minute. They said that 18 players must be named around mid-May, and the rest of the team before June 20th or something like that. They can't change the rules just because Ron Wilson is in the race for the Cup.