Reset your computer's clock to one of these dates to get a special message

Ash Wednesday 8 March 2000
Flag Day 14 June
April Fools Day 1 April
Great American Smokeout 3rd Wednesday in November
Guy Fawkes Day 5 November
Sweetest Day 3rd Saturday in October
Mother's Day 2nd Sunday in May
Father's Day 3rd Sunday in June
Day of the Dead 1 November
Michaelmas 29 September
Bastille Day 14 July
Elvis Presley's Birthday 8 January
Earth Day 22 April
National Coming-Out Day 11 October
Martin Luther King Jr. Day 3rd Monday in January
Saint Patrick's Day 17 March
Easter 23 April 2000
Nurses Day 12 May
Labor Day 1st Monday in September
Yom Kipper 20 September 1999 or 9 October 2000
Independence Day 4 July
Thanksgiving 25 November 1999 or 23 November 2000
Hanukkah 4 December 1999 or 22 December 2000
Valentine's Day 14 February
Christmas Eve 24 December
Christmas 25 December
Groundhog's Day 2 February
New Year's Day 1 January
New Year's Eve 31 December
Kwanza 26 December

These times also produce different messages

Friday after 8pm
Saturday after 8pm
Anytime after 8pm
Anytime before 4am
Anytime between 4am and 9am

And these Holidays too!

Arbor Day
Boxing Day
Secretaries' Day
Grandparent's Day