From what I have seen and based on responses; it is not possible to hide a workflow once it has been created.
You can design one in such a way that it only displays based on specific scenarios (design this before you create the workflow/ process).
You can also frequency in Form and Journal templates.
What we ended up going with was having a dashboard which runs a business rule to identify which period you are in and will switch between interactive dashboard and informative display based on the result.
That is correct. What I do, which might be an option for you is to use a WF Event handler to auto-complete WF's for time periods the WF is not applicable. I define Time filter in one of the WF Text properties to define when the WF should be required or not.
