You can search this site, which has topics, including a fairly recent one which discusses the storage of dates in the repository. Basically its the number of seconds since a date in 1970. There is a simple formula which converts these dates. Alternatively, you can look on the BO cd at the repository section, which provides a similar explaination.
Look at the Supervisor FAQs
Nick Daniels 
(BOB member since 2002-08-15)