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

Markup Text
Displayed as
Today is !today. Today is 20 Jul, 2018.
XML is !today -xml. XML is 2018-07-20T16:37:03.
Right now it is !today -t. Right now it is 20 Jul, 2018 16:37.
Tomorrow is !today +1. Tomorrow is 21 Jul, 2018.
Last week was !today -7. Last week was 13 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.)