Historical clue formulations

• When computers work — 2014-06-29
• Period when a computer is functioning — 2013-08-05
• Working hours — 2012-12-30
• Hours of operation? — 2010-05-14
• Working hours — 2009-10-25
• When surfing is possible? — 1999-03-20
• Computer availability — 1997-05-17