Does instant bitcoin withdrawal mean instant?

I'm curious to know, when it comes to instant Bitcoin withdrawal, does it truly mean that the funds are available for use immediately? I understand the concept of blockchain transactions being processed quickly, but is there any delay or waiting period between initiating the withdrawal and having access to the funds? Are there any factors that can affect the speed of an instant bitcoin withdrawal, such as network congestion or verification processes? And finally, are there any fees associated with instant bitcoin withdrawals that customers should be aware of?