It depends... For a simple PDF file, it should be fast, for a complex one (and that depends on how it was generated), it may take a long time. Do you suspect that your conversion is hanging or are you just curious about other people's experience?
There are certain PDF files, generated from e.g. PowerPoint files that contain 10 thousands of small images. If you want to convert a file like that, it will take a very long time. A one page document with just text will convert in a few seconds.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...