s21 - confused about dates

[Mina]

6 month AST to run from 8 September.
I want to serve the s21 Notice at the same time (although hopefully I won't have to rely on it) - what date should it specify - 7 March or 8th March?

Thanks

[P.Pilcher]

"After 7th. March"

P.P.

[Mina]

Thank you for that P P:)