
My brother's coworker tried to go back to work the day after his booster and fell asleep on the forklift (everything's fine, they sent him home for the rest of the day) so I'd just warn anyone to not make plans for the day after your booster shot.
If you're in the U.S., the government vaccine website will tell you which places have which shots and who has walk-ins or appointments available. I was able to just walk in to the pharmacy in my local grocery store like I did for the last booster.