Note: I have also found that unless I've previously logged into tableau in a that browser, I just get bounced to a login page. Is there a configuration option within server to allow embedded links to come in without needing authentication?
I'm working on a similar problem but wanting to filter a date range rather than discrete dates.
A google search provided me with this helpful PPT doc:
It specifies the date format that needs to be called by the server as
I'm also considering creating a calculated field that transforms the date into a string format that could then be specified.