Let’s do the maths on this.
It takes 48 Tory MPs to write to the 1922 Committee chair to trigger a leadership confidence vote. Hasn’t happened. And won’t while MPs are in their holidays, which last until 4 September.
In the confidence vote if May gets 158 out of 314 votes she stays PM. The majority of Tory MPs voted remain, and none of them trust Johnson. I’m guessing likely she will win.
If she doesn’t pass the confidence vote she has to resign and not stand for the leadership, then there are a series of votes amongst MPs to narrow down the field to 2, who then campaign to win a vote of party members - 8-10 weeks.
So earliest leadership change, unless someone stands unopposed (like May got away with after Leadsom imploded) would be sometime in November.
EU negotiations due to finish in October, so all Parliaments have time to ratify before end of March next year. If there is no deal to ratify you get what you want without a change of leader. If there is a deal, and it is passed by Parliament, too late for whoever the new leader is to change it.