Oh, cool, thanks. I got that far but I'm using google translate and on the "Registro de vacunas" page there's a link to a different part of the website that I thought it wanted me to use...took me down a different rabbit-hole, lol.
I'm trying to get an appointment on the 21st but it's blanked out, looks like we can't make an appointment that far out...I'll try again later.

BTW: the weird think you noticed about Sunday to Thursday is showing up for me and I only use windows. I'm using Firefox, so that might be the issue.