Hello AliB
A Saver Day Pass is good for travel on one day only. In order to use such for your outward and return journey, you would require two Saver Day Passes, one for each day.
Return tickets, being Point-to-point or Supersaver tickets, are good for one day, only. If you would like to buy a return Point-to-point or Supersaver ticket, you would have to buy two single journey tickets, one for each day.
Kind regards,
Roland