Hey there, congratulations on making it to the McKinsey interviews!
The standard scenario is to have a ‘batch day’ per round, meaning you have a day with 2 or 3 interviews of the first round, and then another day with another 2-3 interviews of the second round.
That said, you might get a scenario where the interviews within a round are on different days. This can happen depending on the interviewer availability. From my experience as a McKinsey 1st and 2nd round interviewer, this is more frequent for the 2nd round interviews since APs and Partners have busier agendas.
Good luck to you, don't hesitate to reach out to me if you have questions about the interviews!