The "raspy-voiced trumpet player" on Merv's show
was Jack Sheldon, the guy who sang "I'm Just A Bill"
on a memorable (maybe the most memorable)
"Schoolhouse Rock."
IIRC, on the stations that carried Mike for an hour
the close would come wherever the show was at the
end of the first hour. For the 90-minute stations, the
close would include the guests from the last half-hour.
Merv, OTOH, had the same close for all stations, which
could be disconcerting for viewers in the hour markets,
since they hadn't seen some of the guests. My memory
is hazy because I usually got both shows for 90 minutes
(except that WFAA in Dallas carried only an hour of Mike).
I don't know about Dinah, since she was on for 90 minutes in
the markets where I lived (Atlanta and Dallas).
I do remember that Dick Cavett's 1968 ABC morning show
started at 10:30 AM (ET), but some affiliates joined it in
progress at 11. Viewers who got the full 90 minutes got
Cavett's monologue and first guests; viewers who got an
hour got the theme song, then Cavett in the middle of whatever
he was doing at the break just before 11.
Nevertheless, the hour show has been the rule ever since
Phil Donahue caught on and Johnny Carson cut "The Tonight
Show" to an hour.