When a ship has an arrival time of 07:00 it will be at least 30 to 45 minutes before you can actually go down the gangway. And while the train station is only a few blocks from the port entrance, it is a good distance from where the ship actually ties up to the port entrance. How long 'till the next train? If it isin't too long a wait, you could try it and if you don't make it just take the next one. But it's a couple of hours, I would just relax on the ship and know I could make the next one.
Your return train definitely has to be rebooked; you need to be ONBOARD 30 minutes prior to sailing.
Have a wonderful cruise.