I mean, if you accept that we should have a warning system where the government can communicate with everyone quickly, it does need to be tested. And early Wednesday afternoon is a better time than most. What would you rather them do?
Incidentally, in the UK the test messages could be opted out of, and a lot of people did. Presumably this doesn't stop the government from cranking the level up to unignorable if they wanted to, unless the big phone OS cos sensibly didn't give them that access level.
What are the good uses of a nationwide, rather than local and targeted, alert?