Contemporary music fans are going to need magical powers, like Hermione Granger’s time-turner, in order to take everything in this weekend. Over at the S.F. Conservatory, they’ve got the home-grown, student-run Hot Air Festival Marathon. So if you’re wondering what you might do with that extra weekend day (Sunday) after spending the previous three days listening to concerts, let us suggest this eight-hour marathon that covers everything from world premieres to classics (members of the guitar department in Steve Reich’s Electric Counterpoint) and from violin-piano duos to wind quartets to full orchestra.