Heppner quote from news release:

"We constantly hear management speak about the 'fresh start' for the company following the bankruptcy and the merger," Captain Heppner continued. "The pilots, whose sacrifices and professionalism made this merger possible, have been waiting for their fresh start for nearly a decade. The 12,000 United and Continental pilots are determined to hold management to the June 15 deadline that was agreed upon to conclude JCBA negotiations. If that deadline is not met, we fully expect the National Mediation Board to release us from mediation as we have requested and allow us to exercise our right to self-help."

As JH has stated before, a release does not mean the end of negotiations. In fact it means more serious negotiations as there is now a very real deadline (to management): the end of 30 day cooling off.

So there is no surprise that the NMB would schedule additional dates. What we care about is the start of the 30-day clock.