On the user activity page it would be nice to be able to see what hours of the day a person tends to be active. This would give one a good idea of whether the person is ignoring your answer (or question) or are just asleep and haven't even seen it yet.
For the use case of seeing whether someone may have seen your question/answer, there is a more accurate way: the last active time on the profile page.
For instance, yours currently shows the following:
Note that it's updated at most every 15 minutes, so it may be slightly out of date for very recent activity.
The least person who is relevant to indicate the quality of your answer is the OP of the question, but the community of the site you posted on.
I experienced that even after years I have posted an answer, some people apparantly found it useful (or not), and up-/downvoted my post.
The goal here isn't primarily to help the poster of a question, but to give value for anyone who's researching for the same or a similar problem in the long term.
Also such feature would be very inaccurate, think about people who work in changing shifts.
This would give one a good idea of whether the person is ignoring your answer (or question) or are just asleep and haven't even seen it yet.
OPs are already notified by new answers, comments or other activity on their posts. They are free to ingnore these notifications. E.g. think about a highly active question (maybe posted years ago), not every OP is willing to check the umpteenth response to their question, or they simply don't have the time to do so.
Implementing such would be just wasted dev time for no value.