So far I have one verified gambling account only which is my Stake's account, it was not a long process since my account was verified within few hours only.
Of course the speed of the verification process will be depending on some factors, the most crucial one is the human resources on the platform who are in charge to do the verification process.
The more staffs (both in number and experience) who is handling it = the faster verification process IMO.
I have not done other KYC in other casinos so I have no idea about average speed, but I have to agree that such verification process should not be done in more than 3 working days.
Trusted casino will verify your KYC very quickly provided you have provided correct and true documents. There is no point for the casino to deny the KYC if there is no fault. Why would casino deny anyone genuine KYC and not let them play.
However, there are some scam casino who will use KYC as a tool to deny our payments. They will allow us to deposit without KYC but when it comes to withdraw they may ask for KYC and if the amount is big, they may deny the KYC without any reasons.
This is why it is always advisable to complete KYC before you play in any casino. Whenever it is related to Casino, they will only be strict during withdrawals. For the business to remain in operation, deposit must be more than withdrawal and that is why some casinos deliberately frustrate withdrawal. It is always nice to read the casino ToS as regards withdrawal and KYV before playing.