I'd plan on it taking 45 minutes. You might have to wait up to 20 minutes for a bus, it's a 10 minute or so ride (and that's if you do'nt have to stop at POR as well). Once you get there, up to ten minutes to get off the bus, get through the security line, and through the turnstyle. I'd plan on at least another five minutes to walk down Main Street to the CP, especially if it's your first trip.
Anne