Hello Beatricedv
There is no reduction type such as GA Night, simply select the GA 2nd class.

The GA Night is accountable for international tickets. However, the ticketing system does not consider the GA Night validity. You therefore have to buy a separate ticket Zurich HB to Zug, as you would have to buy when you would travel as far as Locarno or Chiasso.
The GA Night for 99 CHF per year is a real bargain and offers great value for little money. Please understand that there are no further discounts granted such as a free ride to Zug. The 7 PM rule is applied even in the present circumstance.
Kind regards,
Roland