How long can we stay at each stopover? (Day Tour)

It's totally up to you as long as the total travel time is 10 hours. You don't need to tell us in advance, you can just arrange with the driver as you travel. 

We are in the process of updating suggested itineraries. Please take a look around to get ideas :)
https://www.funtastickorea.com/en/course
http://blog.funtastickorea.com/?s=sample+itinerary