Note: This was originally posted by an inactive account. Content was preserved by moving under an admin account.
Originally posted by: aopHi!
You could use something like this inside a filter (here EXCELDATEVALUE is the field containing date in excel serial number format formatted as string):
ConvertedDate=addDate(date(1900,01,00), long(EXCELDATEVALUE)-1, "days")
emit ConvertedDate