When I am exploring through the workbench shared by employer i had seen a setting when I choose Constraints Where Clause of a Feature Reader which asks for Baseline Historical Time. I want to know how this is being set in the transformer.

That's not an 'out-of-the-box' parameter in FME, but rather a user built parameter. Without seeing the workspace itself, we won't know how it is being used. You can right-click any of the user parameters and show the references. That may clue you in to what it's being used for. Alternatively, if you upload a copy of the workspace here we can take a look.