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

Markup Text
Displayed as
Today is !today. Today is 21 Jan, 2018.
XML is !today -xml. XML is 2018-01-21T01:05:38.
Right now it is !today -t. Right now it is 21 Jan, 2018 01:05.
Tomorrow is !today +1. Tomorrow is 22 Jan, 2018.
Last week was !today -7. Last week was 14 Jan, 2018.
The month is !today (MMM). The month is Jan.

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.)