I think China and Korea requires that?
No, it’s three working days. link
Someone told me Korea has 48 hours, I’m not going there so I’m not going to Google it.
It’s three working days, but airlines are interpreting that as three calendar days.
China is two calendar days. (I know someone who just did that. They got their test Friday afternoon and the results were valid till midnight Monday morning.) China requires PCR AND IgM testing (Taiwan requires just PCR). China also makes you get approval from the embassy, which takes some hours. And you have to test again in any layover countries. Just mentioned since you brought up China.