The in-person "interview" is not actually an interview. The interview was buried throughout the lengthy online assessments. If you get an email invitation to the hiring event, you're going to get hired on if you accept the offer and pass the background check/drug test.
Get to the event, wait in the tiny lobby (or more likely outside) with others at the same appointment time. Proceed to check in when called. Make sure you have your ID on hand. This is where they make the offer with your initial schedule. There appears to be a little flexibility in switching shifts/days if available, but not much, so be sure to have your correct availability marked online. Full-time is four tens in a row, either day or overnight.
After that is badge photo, more waiting, and a short overview of the position/benefits while self-administering your drug test. They say to expect a couple of weeks for the results of the test and background check, but it could be a good bit faster.