I don't think verification in centralized exchange is instant, it should be manually checked because it's easy for someone to create a fake KYC. Manual checking is used in order to see if the identity is true what he have submitted, if the face is different then of course the casino or exchange will reject it and ask to retake. Or they will ask more verification in order to more knowing the person behind the account.
It depends on KYC level. For basic level, you will do KYC with software and result is immediately after that but the annoying experience is you will have to do it multiple times. Many times I failed with KYC directly with KYC software that hardly to recognize my face even light is good enough.
For higher KYC levels, your documents will be proceeded manually by Compliance team and it takes a few minutes, hours or days.