Of the twenty five or so schools I'm applying to, I recall only 2 mentioning weekend interviews (and one said this is extremely discouraged since they want u to sit in with students and get an idea of what class is like)
One nice tip is since most interviews can be scheduled on Fridays (and rarely on Thursdays) according to what the admissions people told me, just take a lighter class load on Friday if possible. Think about it this way.. you apply to 15 schools, get 10 interviews.. thats 10 days of Friday class you have to miss and that adds up over a semester. You've got a month left before this semester ends, so try your best to make Friday light
On the upside, I'm told some schools do regional interviews (again some discourage this but this is normal with some schools) and some schools will interview in the month of January when most of us don't have class. However, this is my list of schools and I have no clue where you're applying, so I'd recommend calling the admissions people and cheking out their policies.
-Cantal