A more uncompromising composer than Michael Hersch would be hard to find. The Wien Modern festival presents the world premiere of an instrumental triptych—partly for piano, partly for French horn and cello—that has been 15 years in the making. The faint of heart will quail at the 15-hour running time (5 a.m. to 8 p.m.), but there’s this to say: in subjective time, Hersch’s high-voltage, calligraphic music tends to move much, much faster than by the clock. And the staggering Baroque setting offers no end of visual delights. —M.G.