Hi all. Current MSI here. Feel free to ask questions and I'll respond whenever I get the chance.
Interviews are allotted about 30 minutes, but depends on how long you take. Some interviews go over time, some interviews run short. Two faculty and open file, but that doesn't necessarily mean that your interviewer has to read your file.
For the class of 2021 (so last application cycle), there were 21 interview dates with an average of 25 interviewees per day. A total of 535 interviewed and 103 matriculated. More stats can be found here:
Office of Admissions PLFSOM Statistics.