TfL site read
tfl.gov.uk
Travelcards and group tickets
You can travel as much as you like at any time with a Travelcard
Can I hop on a train before 0430, like the 0410 Stansted Express, and use the benefits of a previous day travelcard with a boundary zone ticket, even if the boundary is reached much after 0430?
- Off-Peak Day Travelcards: use from 09:30 (Monday to Friday), anytime on weekends or bank holidays for the date on the ticket and for journeys starting before 04:30 the next day