Possible Clues:

• Long runs?
• Extremely long stretches
• They're longer than 57-down
• Pig might make them fly enough for the Times
• Vast sweep of time
• Millions and millions of years
• They would give a pig lots of time to fly
• Years upon years
• Lots of time to get the pig to make them fly
• Principals in Eugene Onegin not singing for ages