Related Clues:

• Quite a spell
• One billion years, in astronomy
• Long stretches
• Group of eras
• Grows up
• Consent and Reason, e.g.
• Golden and Bronze
• Series of periods
• Period between blue moons
• Vast time period
• 2001 and 2010
• Geologic division
• Longest division of geological time
• During working hours
• Improves Scotch