I got my processing training and process in dates mixed up. I process in tomorrow on 5/15, while I didn't think I needed to be there until 5/16. If a show up to process in a day late, will there be a problem?
If you can't process in tomorrow you should call or email HR immediately. They are probably gone for the day but will get your message in the morning. I wouldn't just show up a day late without telling them; that could cost you the job.