If you are close to the port you could drop your bags check in then go off sightseeing
Just be back on the ship by 8:30 -9 pm
Make sure O has contact info for you eg email phone # incase there is an issue
If not then show up before 9pm you can have your TA advise O that you will be arriving later in the day
You do not say what port you are embarking but some ports the security people may not be there & you may have to get to the ship from the port gates on your own