Yes you can. The ticket is valid on any train from Geneva to Zurich. As it says on the SWISS website:
https://www.swiss.com/ch/en/book-and-manage/partner-offers/swiss-airrail
The departure time for your train is shown on your boarding pass. Please check the current timetable on sbb.ch or the SBB Mobile app before your departure to take account of any possible changes to the timetable. Your SWISS Air Rail boarding pass is valid on all connections on the relevant route one day before departure and up to one day after the arrival of your flight. For trips to the airport, the scheduled train arrival must be at least 70 minutes before your connecting flight.
So you are not bound to the departure time shown. You can go the day before. The only thing you need to do is not plan on being at the airport later than 70 minutes before departure.