Why can I see some timetable 'slots' but not others?

Hi AndroidOL and Gibbon Community!

I really and truly tried to do what you told me, but this won’t work.
Trying to tie a second ‘Day’ to the ‘Tie Days to Dates’ always ends in this error message:

It’s weeks now that I’m trying to put a ball into a square shaped hole and I’m at my wits end…