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

Markup Text
Displayed as
Today is !today. Today is 19 Jul, 2018.
XML is !today -xml. XML is 2018-07-19T15:51:56.
Right now it is !today -t. Right now it is 19 Jul, 2018 15:51.
Tomorrow is !today +1. Tomorrow is 20 Jul, 2018.
Last week was !today -7. Last week was 12 Jul, 2018.
The month is !today (MMM). The month is Jul.

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.)