You can ring the line as soon as you board for reservations. Some people seem to like the specialty fee restaurants. Personally, I won't touch them. It's way too much food for human consumption in one sitting.
Well I suppose you could eat as much as you want in any of the restaraunts onboard....it's just that Sabatini's on Princess ($20.00 per person) has LOADS of courses that are brought out to the diners.
I know some people rave about it. Everyone is different. I just find it unseemly to pay extra and to have what? EIGHT or more courses of food. It's glutony.
I would eat half as much for half the price, though. I have very cruisey friends who say it's quite overrated too. But others here jump up and down about it.
So again, you can phone as soon as you board and reserve a space. I am sure you will get reservations when you want. The lines may play up the popularity of the speciality places just to get people to book, and to make them worry they won't be able to get a space.
So please, no one jump all over me on this, just my personal opinion.