Then why the deadline of this Saturday?
They let the publication of the Third Secret of Fatima pass a 40 year deadline (explicitly written on the enveloped, by express order of Our Lady") and yet one of the conditions on a split that has lasted 20 years is to "respond positively" by June 28th?
What exactly are they responding positively to by June 28th? A commitment to read the 300 page appendix?
Not necessarily. Each point begins with "A commitment to ..." Clearly, the commitment will need to be defined. We also have to realize that it appears that the SSPX may have had a draft form of these points in their hands for some time.
The Commission has given a month's time from the formal presentation for acceptance on whether the finalization can begin. No one expects the final details to be worked out by then, it is common place to set an expiration date on offers during negotiations. It creates a sense of urgency to keep things moving.
In this instance, the analogy of a job offer applies. The superior party (Holy See) makes an offer based on certain conditions, with an expiration date. This presents the job seeker (SSPX) from dragging it out, hoping for a better offer elsewhere, etc. In short, the deadline offers some prevention of the Holy See looking like a fool.
It's not terribly "collegial" but I see the Holy See taking a harder stance with the bishops, in this case the SSPX.
For example, the meeting with the American bishops agreed to the meeting during the Holy Father's pilgrimage and they probably thought that the USCCB press office would not be summarizing and releasing information. The Vatican took it out of their hands and went directly to TV and then informed the bishops that it would be a live broadcast.
In this case, the SSPX had discussions and then the Holy See published with the proffered terms were publicly, effectively blunting whatever counter-union whisperings about what was taking place.