This is important to know and the reason why I have asked: Saver Day Passes have different rules compared to Super Saver Tickets.
Holding a Saver Day Pass you can use any public transport as indicated on this map: https://www.sbb.ch/content/dam/internet/sbb/de/abos-billette/abonnemente/karte-geltungsbereich-ga-halbtax-stand_d_barrierefrei.pdf.sbbdownload.pdf. It is valid on the day of validity from 12 PM until the next day at 05:00 AM.
In Switzerland, train tickets do not include seat assignments; consequently, a seat is not guaranteed - you pay for transportation only; however, our public transport is mass transit - as suburban trains in other countries. You show up at the station, you look at the departure board for the next train service to your required destination, you board the train, you find an empty seat and you enjoy the ride.
With national trains, seat reservations are only possible for IC-InterCity trains yet absolutely not required. If there is no seat left in a train, you might have to stand until the next station when some people get off and give up their seats.