I do individual interviews, but have been thinking about trying a virtual format since most of my college students come from a school that is about 25 miles away. I prefer individual to group simply because I feel it helps me get to know them better, which helps with placement.
I do have specific times when they can apply for each semester. I also determine a cut-off, based on a number of factors. After a certain point in the semester it is not efficient to place them knowing they will soon be leaving for Christmas break, summer, etc, and class schedule changes will necessitate changing their schedule (and possibly their department) with us.