Our last cruise this past July we arrived at 10.15 (via private shuttle) and were on the line outside the gate that leads to port.
There were about 10 ppl ahead of us and they opened the gate about 10.30
Security was a breeze, had our KTTW around 10.45... we walked in the ship about an hour later (gold, I've no idea what our PAT was)
After this experience, I would def. recommend arriving early. You avoid the huge crowds that start flooding the place around noon.