From the manual, I understand that alerts run every few minutes/seconds checking constantly if the trigger condition is true. When it is, it sends you a message. So you don’t set when it runs, it will let you know.
Have a look at the “Results alerts” trigger condition, that one natively “skips if there are no results” in a question.
So, although, both features are similar and do overlap a little, they are conceptually different and have two different purposes.
At least in my opinion.