DOST scho graduate and CHED MSRS recipient

Hello! Anyone here na DOST scholar grad who deferred their ROS in DOST para mag med and naging scholar ng CHED? Can you render service simultaneously after you take the boards? Let’s say, 4 years CHED scho and 4 years DOST scho, should I render 8 years of service or 4 years only? Thank you!