First, your query seems extremely selective. Give me all the answers to PHP questions from today where the answer has exactly 3 comments? I don't know that you're ever going to find a whole lot of those. Maybe if you change your criteria to CommentCount >= 3
(and go after tags the right way), but even with those fixes, comments on answers don't often get that high (or stay around very long).
Second, SEDE is updated weekly, on Sundays. See this question, this question (which links to this query, which you can use to monitor status), and this question. (It happened to be that just this weekend, the normal refresh failed, but that wouldn't have contributed to this specific issue.)
The SEDE refresh is an extensive operation because the data is transformed in various ways (the structure is simplified to make your queries easier, and the data is sanitized to remove any PII). So on a Saturday, no, you're not going to find any posts there from today (well, after the prior Sunday).
You can just check this query to see why your WHERE
clause is additionally too selective:
SELECT MAX(CreationDate) FROM Posts;
Once you've picked date criteria that work, you can fix the other issues in the query.