We also booked ours thru the website, the same week we booked the resort so we had no trouble getting a time. We bought the passport so we had tix for the Bowfin, Museum, and Missouri as well as the Arizona, and they could be used over two days within a week's time (except the Arizona had to be the time you pick).
We used the directions from the website - it tells you what address to put into your gps to get you there directly, but their directions worked perfectly. We got directions from concierge for a few other locations and they were also direct, no troubles.
We had 11:00 tix and left Aulani at 8:45 on a Wednesday morning. We had no trouble parking by going then, and we had plenty of time to see the Bowfin before our time. In fact, we were queued up just behind the 10:45 group and they had a few extra slots so we got in early.
Be sure to either not take a bag or know you have to check it before entering for $3. It's to the right as you approach the main entrance.