What is a travel day?

A travel day on a Eurail pass lasts 24 hours, from midnight to midnight. When you active your Eurail pass on a day, you use up one of your travel days, and you can use your pass for unlimited journeys on that day.

Night train rule: when travelling on a sleeper train, only the day of departure counts as a travel day on your Eurail pass. For example: you take a train from London to Amsterdam on the afternoon of the 31st of August. In Amsterdam, you change for the sleeper train to Zürich, departing on the 31st at 18:00 and arriving the next morning at 09:00 on the first of September in Zurich. Only the 31st counts as a travel day on your Eurail pass; only one of your travel days has been used.