I'm sure everything about the telethon, from the timing and length of recorded segments and local breaks to which acts were booked to perform at certain times of the evening or day, etc. were all well thought out and planned.
Somewhat unrelated, but I once read an article that the QVC and HSN hosts have a monitor in front of them that shows the number of orders being placed at any given moment so they know when to push the right buttons or say the right thing to cause more interest or generate more sales. It's also been proven that when they use certain buzzwords or phrases, or when David Venable on QVC does his little happy dance, for instance, incoming calls and orders spike.
Similarly, I'm sure the folks running this telethon (and others similar) 40 years ago also had the ability to see the number of calls coming in and the level of $$ being pledged and also knew which types of programming or commentary was most effective.