If you want 366 days in a year you'd have to speed up the Earth's rotation, not slow it down, resulting in shorter days.
I mean, I still have no idea what's going on in this thread so I don't know if that helps at all.
I'd slowing down the speed that Earth revolving around the sun(Revolving Velocity) or making that orbit longer(Revolving Circumference) by moving the Earth a bit further away from the sun(it'll relieve the global warming a bit also).
And what are the people of no religion supposed to do on that day?
It's very similar to the existing Sunday, people can rest or do some other activities to replenish their lives. Not everyone in the United States celebrate every holiday, but most of them get days off.
If no more Mondays, all the pre-defined holidays and their associated activities will go to the next day(Tuesday) just like you automatically get Mondays off when the holidays land on Sundays.
This is how Garfield defines his most important Monday -
https://d1ejxu6vysztl5.cloudfront.net/comics/garfield/2017/2017-06-19.gif
Should be interesting how you guys cope with having a different calendar to the rest of the world. Than again you're still using that archaic measurement system too.
The calendar I post is for a different planet like an Exo Planet, so it won't bother to produce a new "6 days in a week" movie. I'm pretty sure humans have used many different calendar systems throughout the entire Earth history, at least Chinese have the lunar calendar and it copes okay with the solar calendar, I try to combine the 2 up but just for fun.
Party Day is Party Obligatory while other days are Party Optional
Very cool! My "Social Day" already covers the "Party Day". People should have more choices on which types of social obligations they can participate in. No party is completely cost free for every attendant including the host unless there are tax returns offered for hosting more parties. There are more casual and official social programs including dating, nightclub, parade, conference, campaign and charity.
In my old high school, it offered "Earth System", "Biology", "Chemistry", "Physics" and some other electives such as "Marine Science", "Environmental Science", "Physiology" and "Zoology". I was only required to take 2-3 of them depending on the credits.
Party is just one subject of Social Day.
How about
Firstday
Tacoday
Middleday
Baconday
Friedday
Partyday
Restday
We need to cover food, clothes, house, transportation, education and entertainment in balance to keep the society productive. Your production line is mainly foods.
For example, biking and car racing are 2 types of sport also 2 types of transportation equipment which fit ideal on Athletic Day along with other sport activities.