If I just want an overview of Seoul, is a full day-and-a-half enough?

I am flying to Tokyo and will be staying for around 9 days. In the middle of that stay, I am planning on flying to Seoul. I am debating whether I will stay 4d/3N or just 3D/2N. It will be my first time to Korea and there does not seem to be as much to see or do over there as there is in Japan. (Been to Japan multiple times and I never tire of it.)