Most modem/router devices provided by your ISP come with a web-interface, where you can create all kinds of configurations, including scheduling the hours/days where internet is allowed and when it isn't.
The interface to such settings varies a lot per device and ISP, but more often than not it is there. Most ISP's do not block you from adjusting any settings inside their modem/router device. But I encountered the first ISP in 25 years of internet experience who does block those settings, so your mileage could vary too.
If you have a generous ISP, their device could consist of a modem/router/switch. There may even be settings for creating virtual LANs, specific Ethernet ports to disable/enable on separate schedules, etc. Don't count on that though, ISPs provide usually the cheapest/simplest device they think they can get away with.
You could introduce a managed switch between the ISP device and the rest of your network. Then you'll definitely have all what you ask for and more. I'm of the opinion that scheduled network access should be managed on the router or managed switch. More reliable and, if properly secured, practically impenetrable.
