If the ship states that they sail at 6PM then believe me, they SAIL at 6PM and you will miss it if you arrive at 6PM. Usually they require you to be onboard no later than 1/2 hour prior to the sailing time. Also as another poster stated, they go by 'Ships Time" which may or may not be the time of the port you are in so check on that as well. Believe me, you do not want to miss the ship as it is entirely up to you to either get to the next port to meet the ship or find your own way back home. It can be expensive.