What is a travel day?
A travel day is a 24-hour period in which you can travel on trains with your Eurail Pass. It lasts from 12:00 AM (midnight) to 11:59 PM on the same calendar day. On each travel day, you have access to the train networks where your Eurail Pass is valid.
On average, it won't take you more than 1 travel day to go from one European city to the next. For instance, you can travel from Berlin to Amsterdam in 1 day, and travel from Amsterdam to Paris on the next.
With a Continuous Pass, like the 1 Month Continuous Pass, every day in the validity period is a travel day, so you can travel by train every day, if you like! With a Flexi Pass, like the 5 days in 1 Month Pass, you pick and choose on the go which days you want to travel up to the number specified.
When traveling on a night train that leaves on one day and arrives the next, without changing trains after midnight, you only have to spend 1 travel day: the day of departure. If you do change trains after midnight, you have to spend 2 travel days.