Yes, you have 24 months from the completion of the written to pass the checkride. That's why you can't take (or "sit") the ATP written until you are 21, it will expire before you turn 23.
There is no requrement for an instructor's signoff for the ATP written, unlike most other FAA writtens. I guess they figure by that point in your aviaton career you should know if you're ready. You just need to present your ID and the license that authorizes you to take the test, either a commercial or foreign ATP. There did used to be a requirement that you have the 1500 hours before the written, you'd go by the FAA office for a logbook audit, get a form and then go to another FAA office to take the test. That requirement went away sometime after 1983. And the days of the FAA conducting the writtens (for free) are long gone. I think I did 10 writtens in room 200 of the old FTW FSS.
Last edited by MarkerInbound; 2nd Jan 2013 at 23:51.