Late September to mid-November is a transition, not one fixed foliage peak. Cooler nights change deciduous trees, but colour develops differently by elevation, latitude and weather. Mountain landscapes can turn before lower and southern settings, while wind and rain can shorten strong local displays.
The route is built around that variability. Seoul introduces autumn in palace gardens; Seoraksan expands it to mountain scale; Andong and Gyeongju place colour around lived and archaeological heritage. Busan provides a southern finish, not a foliage guarantee. Every stop retains cultural value if colour arrives earlier or later than expected.