Possible Clues:

• 'Falstaff' and others
• Plays in which the words are sung
• 14 across for work and song
• "Einstein on the Beach" and "Nixon in China"
• Met set
• 'Doctor Atomic' et al.
• Might music make short work of long times?
• Works with singers
• Work for 15 across 18 down, perhaps
• Times of work for music