FitNesse. UserGuide.
TodaysDate [add child]
To diplay todays date:

Markup Text
Displayed as
Today is !today. Today is 16 May, 2012.
XML is !today -xml. XML is 2012-05-16T16:40:03.
Right now it is !today -t. Right now it is 16 May, 2012 16:40.
Tomorrow is !today +1. Tomorrow is 17 May, 2012.
Last week was !today -7. Last week was 09 May, 2012.
The month is !today (MMM). The month is May.

As you can see, you can add or subtract days. You can include the time tiwh -t. And you can use your own format for the time. (See SimpleDataFormat for the syntax.)