Well, goin' back to Ennis's flowery
writin' style (you bet) maybe sumthin' like:
divorce over, movin' this weekend.
I can see Jack readin' this and almost jumpin' into the pickup, thinkin' he an' Ennis will be all alone at Ennis' new digs.
Course he doesn't know where he's goin' but figures he can find out.
A few days all alone w/Ennis, in a house! with a bed! (well maybe) Whoee!
But of course in the movie it takes him a few weeks to accomplish this, as Ennis musta' had those few weeks after the divorce where he missed having the girls with him, etc. So the elapsed time here is not just a few days. Do I have have that timeline right CH?

Jackster, this is a tricky one - maybe an impossible one - in part because we have such little information about the divorce in the short story. All we get from that is that "...when Alma Jr. was nine and Francine seven she [Alma] said, what am I doin hangin around with him, divorced Ennis and married the Riverton grocer."
Ossana and McMurtry dramatize this by showing us the divorce court scene which concludes with the judge saying "...Del Mar divorce granted, this 6th day of November 1975".
In the movie this is immediately followed by Jack's drive up to see Ennis. However, there is no detailed description of this trip in the ss though we are told that Ennis phoned Jack to tell him about the divorce and that Jack "had misunderstood the call, had driven twelve hundred miles north for nothing".
We know the divorce was granted in early November but what month are we in when Jack and Ennis meet? We know that the divorce was granted in early November and that something like two months must have elapsed after that for Ennis to have missed at least his first weekend visit in his new quarters from the girls. So are we now in January? That, however, doesn't quite jibe with Jack's departing line : "I'll see you next month, then..." In February? In the mountains of Wyoming? So maybe we're in April or May? But if that is the case then a considerable amount of time has elapsed between the granting of the divorce and the postcard.
I think the best anyone can do is imagine that Ennis spent some months getting everything sorted out and the dates for the children's visits arranged before sending Jack that postcard. There is some textual support that we are now in April or May as one of the earlier scripts has Jack saying "I'll see you in the first week of June then" but obviously the reference to June got dropped by the final script.
Somebody once suggested that what we see in the movie is an "interlocutory" decree and not the final decree which came later but, in either case, time has to be allowed for at least one missed visit from the children before Ennis sends the postcard. Unless, of course, Jack waited awhile after receiving the postcard before setting out but that doesn't really square with his "excitement".
All in all, I suspect this is one of the points in the timeline where being definitive is impossible. However, I still enjoy speculating even if it does lead to a dead end.