The express buses for (Yangon to Mandalay) depart from Aung Mingalar Highway bus station in Yangon which is about 7 km (20 mins drive if no traffic jam) from Yangon International Airport and 19 km from Sule Pagoda which is a central area of Yangon city. It may take about 1 hour to 1:30 hours from Sule Pagoda depends on the traffic condition.
The express buses for (Mandalay to Yangon) depart from Kywe Se Kan highway bus station in Mandalay which is about 8km from Mandalay Railway Station which is considered a central of Mandalay. Due to traffic, it may takes about 30 to 45 mins drive from around Mandalay Railway station area.
Chan Mya Shwe Pyi (a.k.a Kywe Se Kan) Highway bus station map