This is certainly the case. I have noticed this in voting patterns as well. I often comment strongly in favor of EU regulations (I believe capitalism is fairer and benefits consumers more with stronger regulations). During times the US is asleep such comments often get a lot of upvotes. During times where EU and the US are up, there seems to be much more contention in the voting, with votes swinging up and down a lot.
By the way, I don't think this is a good way of voting. IMO comments should be upvoted if they provide good insights (even if you disagree with them) and downvoted when they are low-content/trolling/full of fallacies.
I regularly have posts that go from say +10 in the evening to -5 in the morning (I post from the EU). I mostly agree with your observations. That said,
> IMO comments should be upvoted if they provide good insights (even if you disagree with them) and downvoted when they are low-content/trolling/full of fallacies.
Votes are not a popularity contest. Only you see your score, and it does not matter one bit whether you have 2 or 20 upvotes on a post. Even moderate negative scores don’t matter. The grey threshold is more important, and you have to post something quite bad to end up there. I think I read a good post that was dead once.
The system is working and the end result is what you want. Sure, it could be better, but we are never going to get a perfect implementation because humans are social animals, and not always very rational.
By the way, I don't think this is a good way of voting. IMO comments should be upvoted if they provide good insights (even if you disagree with them) and downvoted when they are low-content/trolling/full of fallacies.