Originally Posted by DFB_london

Not quite. There were a few hundred 'pilot scheme' codes issued to the UK. The number was very limited and not available to all applicants.

This was test scheme: unless you were invited into it - with a unique code - the rule you state above does hold true (for now). The good news is that if the test goes well, then maybe things will open up.

The very limited number of codes were distributed to the most frequent UK-US flyers by the powers that be - including via GGL. These were distributed based on previous flying/INS patterns and were offered, not requestable.
(Just to be clear, at present you have to be asked, you cannot ask to join.)

In terms of the OP question: Once you have registered, got your police cerficate (aloow 4 weeks), paid the US$100 it can all go v quiet for several weeks. Once the background checks are complete (you will need to list every country you have visited and when), you will then be told you have reached the stage where you need to attend an interview with INS at a US airport where they have a CBP office. You can book this online. This, if all goes well and is successful, will see you registered. All in all allow aorund 2-3 months assuming you visit the US a lot to enable you to complete the last bit.

Overall, I have to say its a travel changing experience. Plane door to cab in 5-10 mins is very possible - even at JFK.