Related Clues:

• Proterozoic ___
• Geologist's unit
• Many, many epochs
• It's a long time
• Very long period
• Immense time span
• Holocene, for one
• Length of a boring class, so it seems
• See husband manage to retire in time
• Making this date is of great importance
• Christmas almost set up in plenty of time
• It's hard to manage looking back for an extended period
• Age record pursued by old companion
• Trotsky missed out on Liberal period
• Clear speaking