I regularly travel home from work from Chessington South, and am aware that if I manage to tap in on my Oyster PAYG before 16:04, I can get the off-peak fare to Wimbledon (£2.90 vs £3.90 saving £1 on each journey).
However I have to travel to Canons Park to help an elderly relative. So I can route either via Zone 1 (Chessington South – Waterloo, and then Jubilee to Canons Park), or via London Overground (Chessington South – Clapham Junction, (pink tap-in) Clapham Junction to West Hampstead and finally Jubilee to Canons Park). The difference being £8.40 vs £3.10.
So my question is that if I manage to tap in before 16:04, and route via London Overground, can I get the whole fare at off-peak rates as I technically started the journey in the off-peak?