I have a business trip where I have an opportunity to spend the weekend in Korea before heading to China in April.

I'm looking to fly to Jeju for the weekend, flying on Thursday evening. Currently, the flights on my date is very cheap (~KRW 50,000) on both Jeju Air and Easy Jet. I'm not exactly sure what time I'll be done with work on that day. Is "standby" possible? I may potentially get there for a 4pm flight, or maybe 6pm or later. Should I wait? Or should I just order my ticket now? Any problem with foreign orders with foreign credit card on Jeju air and Easy Jet?

Another thing I'm worried about is how reliable are flights leaving direct from CJU to China. Specifically CJU - SHE (Sunday 1 flight only!) and CJU - XMN (Saturday, 1 flight only!).