The chance of trying to speed run the nominee before the election is slim. It puts the senate R's into a huge unknown that's easily avoided by punting to after the election.
It's more advantageous to Trump and the R's to milk the fight for enthusiasm/fund raising while taking any potential hit during the lame duck session, where there's little accountability to be had.
It also leaves what time is left on the calendar clean for the CR to avoid a shutdown. Plus any potential for a covid bill would die. The idea some of these senators will park themselves in DC the weeks before voting isn't going to work.
the White House has already acknowledged that even with the fastest time frame it likely couldn't be done before the election. If attempted the vote would literally be within a stones throw of Election Day, which is an awful scenario politically.
The signaling from the white house to mitch is that he controls the time table. The plan is already in, regardless of what you'll probably hear from trump as he tries to use it for votes.