I believe that you are confusing the Regular Trading Hours (RTH) setting with the Time in Force (Day / Gtc).
Globex stop limit orders are native to the exchange. This means that when the order is entered, it is not held within the IB system until triggered. The order is sent to Globex and the exchnage holds and handles the triggering of the order. As a result of this, the RTH setting does not apply because every time you enter a Globex stop limit order it is sent natively to the exchange and will trigger at any time the product is trading.
In the Web Trader "Create Order" window, you will see a field labeled TIF (time in force). This is where traders specify whether the order being entered is a day order or a GTC order. The default selection is DAY but you will see that GTC is an option in the drop down menu.
I hope this informaiton was helpful.