I'll give you my 2 cents since no one else has responded. I have only taken 2 HAL cruises (Amsterdam'06 & Zuiderdam'04) so there is a bit of memory work involved here. There is a Lido pool area with BBQs/pizza and there is the Lido buffet. The pool area is open all the time but the pool and hot tubs are netted over at night. I never used the BBQ/pizza pool side but I believe it was only available at meal times. I prefer not to hang out at the Lido pool because of the high amount of smokers. The aft pool area is the place to be. Out in the open with the breeze in your hair.
The Lido buffet is open for coffee/tea/iced tea/water 24 hours but they do not serve meals 24 hours. But I remember snacks being available all the time (I try to stick to 3 good meals when on board to avoid to added weight gain) (but that does not work, could be the amount wine consumed).
Finally getting back on a Dam ship, Nieuw Amsterdam Nov'11 (My Mom's 80'th B'day cruise)
Navigator of the Seas 2010
Serenade of the Seas 2009, 2011