Also unless you're walking around the interior of the ship all day long then you aren't wearing your mask for the majority of the time. For example:
Leave cabin wearing mask to go to breakfast/lunch/dinner. Once seated remove mask to eat. However in the buffet you should wear your mask when going up for more food etc. After your meal put your mask back on before leaving your table.
If you go outside to the pool you can take your mask off.
If you go for a walk around the promenade deck you can take your mask off
If you go to one of the inside bars you can take your mask of while seated.
Some venues are "sip and cover" like the theatre and lounges where there are shows or events like trivia or bingo. You're not there for hours on end, most of these events are 45 minutes plus a bit more if you get there early to get a good seat.
During a whole day, for us 8am to 11pm-ish so a 15 hour period, I estimate we wore our masks for only around 4-6 hours in total depending on whether we went to a show or not. Maybe a little more if the weather was too unpleasant to go outside.