That's peculiar. My side effects began six to eight hours after the second Moderna shot, and continued for several days.
Mine lasted 18-24 hrs. And started in your time range. Except for the sore arm which lasted 2-3 days.
Then came the thingy 21 days later. I don't recall ever having the Flu come on exponentially, and last just 18 hrs. It came suddenly, and left suddenly. As opposed to a usual slow onset, and 3-5 day recovery for the Flu.
For now I'll claim to had the 18 hr Covid. Short circuited by the immunity provided by the Moderna vaccine. Unconfirmed since I didn't run in terror to the EMR for a Covid virus test on a Sat night.