The "latest" you get off the ship is a cruise line policy issue, not port dependent. I would expect 10am at the absolute latest, probably they will be doing last call by 9:30.
They will start allowing people off when the port approves. I would expect by 7am, if not a little earlier.
The questions about Immigration and Customs need more info, as asked above. Last time we were there, we had sailed from another EU port, so we just did a passport check, no Customs. But there was only two officials to check 2000 people, so the line was long. The official I got wanted to chat, as my last name implies Dutch heritage (its actually been altered by Dutch Immigration in the 1880s when my relatives came over, passing through the Netherlands).