What is a "Post"? Are you talking about a forum post here or something else? A timestamp is vital metadata, so why would you want to hide or change it? Any change would invalidate everything (e.g. who had an idea first, answer comes before the question was even asked, etc.) so I sure hope it cannot be done, even by a moderator. Please explain why you would ask a question like that.
Maybe I am completely misunderstanding your post. A few more words would have probably helped.