What is a travel day?
A travel day lasts 24 hours from midnight to midnight. On each travel day you have access to the train networks where your Eurail pass is valid.
7 p.m. rule
When traveling on a direct night train that departs after 7 p.m. (19:00) and arrives at its final stop after 4 a.m. (04:00), you only need to enter the arrival date in the travel calendar, even if you leave the train before 4 a.m. This way you get 5 hours of travel for free. This is known as the 7 p.m. rule.