Internet speed slowing after midnight

I’ve had cox preferred 150 for a while now, and I’ve periodically noticed speeds slowing after midnight. Videos and streams I often watch in 1080p60 are buffering or choppy so I have to lower the quality. My ping in games is higher and fluctuates sporadically, while during the day it remains exactly the same.

I normally don’t game late at night, but I’m out of work on sick leave and noticing it much more since Friday. Every night, without fail, after midnight I start having connectivity issues. Webpages load slowly, videos buffering, games lagging or becoming periodically unresponsive. 

I’ve noticed there’s many other posts about the same exact problem, so I’ll just add to them for visibility. 

pretty sure nothing will be done about it, cause I can’t count how many times I’ve been told to get a new modem even though the one I have works perfectly fine for 80% of the day.