To be honest, it really depends on the source.
If your source is compatible with HLS protocol (h264/aac) and you enabled quick option while adding the video, then it can be really REALLY fast. Like, in minutes.
But if your source is (for example) 4K hevc/ac3 and you decided to disable quick option while adding the video, then it can take a while. Up to 2 hourse, depending on the server’s CPU.