If you are building your aquascape in the open air, you can substitute cement for the epoxy as the glue between rocks. I use a thick cement paste for this and I like it better than epoxy because I find the cement has better structural integrity. Technically, Portland cement takes a week to cure with light mistings every now and then and six weeks to six months of soaking to stabilize the pH. If you're just using a small amount here and there as glue, it shouldn't have much impact on your pH. If you want it to be tank ready faster, you can use BASF Emaco s88ci cement which will cure and be pH stabilized in a week.
Oh, and if you decide to go this route, you will still want to use acrylic rods to be the backbone of your structure.