As anyone who reads this site regularly already knows, the Oyster fares system is ridiculously complicated. There are odd scenarios, particularly in the afternoon peak, where it can be cheaper to finish a journey in zone 1 than at the zone 2 station beforehand. However, this evening I’ve found a case where the cheapest route varies depending on the time of day you travel.
An example is Dartford to Highbury & Islington. Forget the really expensive route via London Terminals and the Underground, but there are two alternatives: via New Cross and Shoreditch High Street; and via Stratford. Shoreditch is in zone 1 whereas diverting via Stratford avoids zone 1. In the peak common sense prevails and the zone 1 route is slightly more expensive (£7.00 vs £6.40). Travel off-peak and the reverse is true (£4.00 vs £4.20). You may well be wondering why. Travel via Shoreditch is wholly on National Rail while the diversion via Stratford requires either Underground and/or DLR. Unlike within zones 2-6, from Dartford there is a premium for mixing travel in zones 2-3 as well as the usual zone 1.
It really is madness.