Keep in mind, that like Via Napoli when it opened, Hacienda doesn't have pacing down quite yet (as seen when I received my entree after one tortilla of my Queso Fundito). In the same sense, they likely are spacing reservation slots further apart than necessary.
In other words, this is my long winded way of saying "Keep trying as more reservation slots are likely to open up as they tune and tweak the timing."