I would do it Julian Date format:
Many applications (especially mainframe systems) store dates in the Julian format, which is a 5 digit number, consisting of a 2 digit year and a 3 digit day-of-year number. For example, 24-August-1999 is stored as 99236, since 24-August is the 236th day of the year. Excel doesn't support Julian dates directly, but you can use them with only a few fairly simple formulas.
How do you write 20th of May 2011 in 5 words without using letters
2 answers
how to write June 1, 2011