I have a Z23 travelcard on Oyster- it was a lot simpler when I had a paper travelcard 🙂
According to the Fare Finder, there’s only one possible fare from Putney Rail to Golders Green Tube, and that’s via Zone 1. However, to avoid Z1 I could change to the Overground at Clapham Junction (and tap the pink reader), exit at Camden Road, walk to Camden Town and get the Tube to Golders Green.
But this excellent site shows that Camden Road – Camden Town is an OSI with an interchange time of 20 minutes- does this mean that if I tap in at Camden Town within 20 minutes of tapping out at Camden Road I’ll be charged the Z1 fare irrespective of my route? But if I wait more than 20 minutes, it’ll be counted as two separate journeys, neither of which enters Z1 which is what I want?