Auto reboot or 3rd party firmware

I'm not aware of any third-party firmware that will run on the Orbis, nor any way to schedule an auto reboot from within the provided firmware. You could try plugging them into a smart outlet, and that would work for at least turning them off, but once the wifi is down, I don't know that you'd be able to remotely power them back on with a smart outlet.

You could go low-tech and try something like a Clapper, or even just a lamp timer set to turn off in the middle of the night for the shortest interval. Ones with little pegs or switches to schedule the on/off times generally have half-hour intervals. You can probably find digital ones that let you set them to the minute. Note: you can also remotely (but not automatically) reboot the Orbi (both router and satellite, I think) via the Orbi configuration page, and also probably via the Orbi app.

But, you might try looking into which device(s) are causing the network slowdown. It could be a device downloading updates, malware, a botnet participant, apps sending lots of data (bad updates, sending queries constantly, syncing large numbers of files, etc.), or even an unauthorized device on the LAN. It could even be an authorized user streaming or downloading a lot of content (e..g, a kid watching porn, streaming video, downloading software, etc.). You could use a packet sniffer to figure out which device(s) are hogging all your bandwidth, or try testing it by removing or powering them all down, and then testing individually to see which one is using all the bandwidth. Remove/disconnect/power off everything but device A, see what the load looks like, then remove A and add B, etc. Some smart devices create an absurd amount of traffic, so it could be one of those, too. Many possibilities. Unfortunately, the traffic meter in the Orbi only gives aggregate data, so, short of resetting it (the traffic meter) every time you test a single device, it won't be of much use to you. I'd probably try a packet sniffer like Wireshark, unless you really want to get in the weeds, in which case, you could do some net flow analysis using something like SiLK, or run your own DNS server, like Pi-Hole on a RasPi, both of which should give you a good idea of the volume of traffic and its origin. Selective interchange is simple and free, but could be time consuming, depending on how many devices you have. All the software I linked to is free, but may not be easy to use, and except for Wireshark, require some knowledge of Linux and a(n at least temporarily) dedicated device, plus a learning curve for the software itself.

Ultimately, identifing and remedying the source will give you a long-term fix, rather than just restarting the Orbi every day.