Historical clue formulations

• Significant periods — 2026-04-28
• Big times — 2026-02-21
• Time periods — 2025-01-09
• Long stretches — 2022-02-08
• Pleistocene and Eocene, for two — 2013-12-23
• They last a long time — 2006-08-02
• Times to remember — 2006-04-09
• They're shorter than periods — 2005-06-03
• Long times — 2005-05-02
• Historical periods — 2005-02-02
• Noteworthy periods — 2002-06-19
• Period pieces — 2002-01-26
• Ages — 2000-04-27
• Eras — 1995-03-12