However, if your client is written in some other non .net language, then you may need to know what exactly the date is.
WCF dates are specified as the number of milliseconds since the 1st of January 1970. This is also sometimes referred to as an Epoch Time Value. The guys over at Esqsoft have a handy web based Epoch date time converter. Great for finding JSON date values to put into a request into Fiddler for testing.
So lets take today's date - 11th October 2011, and convert it to an Epoch Time Value:
is our output value.
Lets see this in the context of a JSON request:
As you can see, we need to wrap the Date in an escape sequence, and then a Date object. We also append the date with our time zone. In my case, I am appending a +0100 as I am one hour ahead of Greenwich Mean Time, currently on British Summer Time (although you wouldn't know it looking at the weather!)
Bertrand Le Roy's blog post on WCF JSON dates http://weblogs.asp.net/bleroy/archive/2008/01/18/dates-and-json.aspx