I bough RS London book and love it but confused if Evensong ends end of August..we will be there September 8!
Looks to me like it's at 5pm every day except Wednesdays September through April.
Evensong is a regularly occurring service that isn't seasonal...it is offered every week on a regular schedule.
Sometimes there is a special service and you will be refused admittance--having to do with commemorations, etc. Perhaps check the Abbey website a few days before.
And if you can't enjoy it there try St. Brides.