When on a cruise ship and being served by a waiter it's a good idea to tip the cruise ship waiter at least $5.00 at the end of the day when they bring you the last meal for the day.
Of course you can tip them the $5.00 at anytime of the day when they bring your meals.
You'll usually have the same waiter come to your door 3 times in the day to serve you your meals and they are very hard working people.
The waiters don't make all that much on a cruise ship so it's best to tip them on the cruise ship at least $5.00
I usually tip the waiter $10.00 per day if they are very friendly because I know they are not making that much money and when I'm on a cruise I budget for those tips.
It's worth it to me to pay those cruise ship waiters more than the minimum tip for the amount of time I go on a cruise ship which is not very often.