The E tickets you are being sent say August 20th, but rest assured they are valid for both the 20th and the 21st.
Please do NOT arrive at the circuit prior to 4.30 PM on Saturday. This will give time for the Tin Top drivers to depart, as they will be occupying your parking area on Saturday.
The meeting details can be seen here: Event Page: https://brscc.co.uk/events/c1-endurance-race-weekend-at-brands-hatch/
Final instructions and entry lists will be published later.