Does doing SEO Activities in Day or Night affect a USA-based website?

It doesn't matter

SEO activities can be done at any time of day and the effects will generally be the same regardless of when these activities are performed, as long as the activities are done properly. However, if you are targeting a USA audience, it is important to take into consideration the fact that the majority of internet activity in the US occurs during the day. Therefore, you may have more success if you focus your SEO activities during the US day time hours, as opposed to the night.

SEO activities are a long continuous process. Changes made will only be implemented in search results once a bot has crawled the site. Compare it to placing a backlink, which is only valuable for the SEO after a bot has visited. The time for optimizing is not important at all.