Tuatara

These are good questions!
 I know I have one virtual visit day that is 3-8 with a clear schedule. We are talking to graduate students and 3 different professors. The other one I have is listed as all day, but no schedule yet. I have no experience with these either, so I plan on being prepared with their most recent published research/their research interests, and my elevator pitches on things on my CV. ALSO make sure you are asking them questions YOU need to know to make a decision, too. They're selecting you, but they also want to recruit you so you ultimately select them. 
But based on some things I have listened to or read, I imagine even an all day recruitment event will be interviews throughout the day with breaks from zoom built in. But I don't know for sure. Each school seems to be going about this process differently. 
 
Does anyone have any tips for partner interviews? I have had really bad experiences with them in the past and I am really nervous. 

Congratulations!
Normally the visit day is for you to get to know the school and program much better, and for professors and grad students to get to know you.
You will be told information about the classes required for the program, graduation requirements, funding, housing. You will get the chance to talk to the grad students and ask them questions.
Then usually you will have one on one or group discussions with the professors. They will ask you about your research and you can ask them any questions you want. It's best to do thorough research on the professors' research and CV. 
And, I almost forgot, in the in-person ones, you would normally be given a tour of the campus. Don't think that will happen during the virtual visitation day