Related Clues:

• Quite a long time
• It's longer than an era
• Big time division
• Span of epoch proportions?
• Extensive period
• Immeasurable time
• Billion-year time period
• One billion years, geologically
• Humongous span
• Annoying wait, facetiously
• Untold eras
• Inconceivable stretch
• Very long interval
• Long while
• Extremely long stretch