@Brian427 You need to turn on professional hosting tools and use the colorcoded rule sets. https://www.airbnb.com/help/article/2499/how-can-i-use-professional-hosting-tools
You will create a rule set for a 3-night minimum and select the low season dates you want to apply it to. Then create a rule set for a no check-in except Saturday and a 7-night minimum and select the high season dates you want to apply it to.
Keep your default settings as the default and always make changes with the rulesets. Every time you apply a "rule" make sure to look at your live listing page (from the guest perspective) to make sure the calendar is allowing bookings as intended. Sometimes you will have to play around with it.