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

Markup Text
Displayed as
Today is !today. Today is 22 Apr, 2018.
XML is !today -xml. XML is 2018-04-22T06:46:31.
Right now it is !today -t. Right now it is 22 Apr, 2018 06:46.
Tomorrow is !today +1. Tomorrow is 23 Apr, 2018.
Last week was !today -7. Last week was 15 Apr, 2018.
The month is !today (MMM). The month is Apr.

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.)