The ZIP format started with MS-DOS dates, which start in 1980. Other dates
have been layered on, but the ZIP file handler used by Azure websites still
relies on the MS-DOS dates.
Using the Unix epoch here (1970) results in ZIP entries that (e.g.)
OSX `unzip` sees as 12-31-1969 (timezones) but Azure websites sees as
01/01/2098.