Time of day issues tend to be other peoples traffic competing with yours. We will assume it is not inside your house so this likely means it is one or more of your neighbors. This is not a very common issue now days the bandwidth you share with neighbors is huge..many times at least 2.5g if not 10gbit the upload speed tends to be 1gbit. It would have to be multiple neighbors doing something crazy at exactly the same time.
What I would more suspect is you are getting packet loss.
First I will assume you are not testing on wifi. That is subject to interference and you can get random issues.
I know nothing about that router. It is unlikely the router is the issue ethernet is pretty simple and unless you were doing some QoS or firewall stuff on the router the router does very little other than NAT and that is done with a hardware assist. Even low end routers can do 1gbit and higher end ones can actually really do 10gbit.
What I would try first is test directly plugged into the modem. You likely will have to reboot the modem every time you change what you plug into it. This should eliminate the router as the cause but it would be highly unlikely a router would have issue at the same time every day problems tend to be random. You do this test more to expedite your call to the ISP and them trying to have your reboot routers etc etc.
If you see issues with the modem connected I would check the logs in the modem. A very common IP to access the modem is 192.168.100.1 but I am not 100% sure on your modem. You likely also can find the signal levels and many a screen that shows packet errors. This is doing the ISP job for them. You can find the recommended levels if you search. They vary a bit depending what type of docsis encoding the ISP is using where you live.
So if this still shows nothing I would do the standard let a constant ping run to 8.8.8.8. Maybe you see packet loss. Bad signal levels will also cause packet loss. If you see loss I would call the ISP. Without the router in the path there is not much other than their equipment that can cause the loss. If they are idiots and try to blame google 8.8.8.8 then you need to do tracert and ping their router instead but I have never heard of a issue ever with a ping to 8.8.8.8 since it is not one server it is duplicated in many cities so if one has issue another takes over.
What kind of router would you reccomend for Spectrum Internet? I ended up getting a Motorola MB8611 modem in hopes of fixing the intermittent internet problems between Noon-6pm on a daily basis dropping frames on my livestreams to twitch, but that didnt seem to fix anything. I'm not sure if it's my router / Spectrum or what at this point.
I even tried the ping -n 100 1.1.1.1 and ping -n 100 8.8.8.8 at the time I was dropping frames and ran speed test on both Spectrum's website and the speed test on Ookala and it showed normal no packet loss drops but my OBS was showing red bar and dropping frames like crazy...
Could it also be my PC? I couldnt imagine it could be that at all but
Ive got a
Asus TUF Gaming OC 4090
MSI MAG Z690 Tomahawk WiFi
i7-12700k
Crucial Ballistix 3600mhz CL16 ddr4 (2x32) 64GB
and I have a 1300W MSI MEG PSU
if that matters at all.
And bitrate in OBS is set to 4500
I'm getting 40mbps upload when it's looking "normal" "good"