Historical clue formulations

• Every seven days — 2013-02-21
• Every seven days — 2009-10-15
• Hebdomadally — 2007-12-27
• The Beatles' "Eight Days ___" — 2004-06-29
• Thoreau's "___ on the Concord and Merrimack Rivers" — 2003-09-05
• "Eight Days _____" — 1994-08-14