I'm only speculating . . . but I'm pretty sure Mayo did the pre-session patter and started and ended the session. That much we can probably assume.
Then . . . LRH (1) wresting control of the session at some point and (2) doing some sort of penetrating analysis mode, a bit of (3) stream of consciousness mode, and then followed by (4) lecture mode before the final that's it, end of session.
Certainly no disrespect whatsoever meant toward Mayo, RIP. Mayo was auditing/researching "on the fly" on a troubled and very ill LRH much of the time, as opposed to auditing on a shining set-up case.
An example of this approach could be heard in the
Battle of the Universes recorded session (1952). The one with MSH as the then-budding "whole-track research" auditor. He was always interrupting and schooling her during the session. I have a hunch he would always be that way, that is, only half "in session" and half wrestling control. Seems like the type.
I'm only guessing, speculating since the subject came up. Interesting to speculate.