Sorry, I was talking about the Join button on the select party screen, not the Join button that gets you to the select party screen.
Of course, you could save some time by already being on the select party screen when the queue opens, but it's just not very practical.
In my situation it could be advantageous. I have a large group and a teenager who I don't know whether or not she will drag herself out of bed to be physically in the park at 10am. So "select all" may not be an option. If I could prep the phone at 4pm the day before with the group, I could save precious seconds at rope drop.