The Show data outside of regular trading hours item in the TWS Chart Parameters window is greyed out when no outside of regular trading hours session is available for the product in the chart.
You can check the trading hours for a product by right-clicking its ticker row in TWS, and selecting: Financial Instrument Info, and Description_._
If you do not see an item, click on the arrowhead at the bottom of the menu to expand it and view all selections.
Find out more about TWS charts in the TWS Users' Guide.