You can make as many journeys as you like in one day. The passes are restricted by days, not journeys. A day is classified as 24 hours commencing at midnight; as soon as you get on a train during the day, it counts as the start of a day’s travel.
Note: OVERNIGHT TRAINS: Traveller will enter the day of departure and you only use 1 travel day when travelling on a direct overnight train that arrives at its final stop after 4AM the following day, even if you leave the train before 4AM. Travel after midnight still counts as day of departure.