Republic of Korea Visa portal1's B-2 visa requirement says... 2
Visa Free Entry for foreign transfer passengers
Besides the passengers for transit mentioned above, those transferring through the Incheon Airport and taking part in the Transit Tourism Program on their way to a third country or the country of their nationality (hereinafter referred to as "general transfer passengers")
Condition of Permission
General Transfer Passengers: Possessing a transfer ticket and staying in the Seoul Capital Area for up to 72 hours
Seoul Capital Area is usually Seoul, Incheon, Gyeonggi.
So you can legally stay in Korea for 72 hours. Note that It is (by definition) different from B-2-2 (Tourist / Transit (Jeju)) visa. Since Jeju Island is an autonomous province where they have more lax visa requirement, visa policy is bit different. Of course, best way to confirm is to check with Korea embassy in Cambodia.
1: Click "English" at the top, then "Short Term Visit", "Tourist / Transit (Jeju)". Link defaults to Korean website when I try to visit, but maybe because my IP is Korea.
2: I said visa, but you're still visa-free.