Beth, Sounds like your mix was too wet. Always throughly combine your dry ingredients so they are one consistent color. I always use sand in my mix regardless of which recipe I use. I sometimes use the sandy gravel out of my creek and have been doing it for years and haven't had a problem. You want a dry mix, think hamburger patties. It should hold together without crumbling or dripping water. You should be able to unmold a 12" to 24" round planter in 24 hours, depends on your temperature. After filling the mold, place the planter in a plastic bag, seal it and place it in the shade to cure for 24 hours (Day 1). Unmold, clean it up with a wire brush or scotchbrite pad and rinse with water. Put back in the plastic bag in the shade(day 2). Let it cure in the bag for another day, spray water inside the bag if it's a very warm day. The next day (day 3) take out of the plastic bag and place in a water bath for a few more days, change water every day.
You really don't need to let the mix sit for 10 minutes.
Most of the time I use equal parts no matter what ingredients I'm using. I usually use cement, sand and peat moss. I use a vermiculite recipe when I want a whiter, sparkley look and I use perlite for a lighter weight recipe. Throw some sand in your mix and try again, good luck! Billie

Beth...

and don't forget to pack, pack, pack your mixture into the mold -- it doesn't get "poured" in like regular concrete, and also mix, mix, mix the dry ingredients as the Portland must be completely incorporated over the particles of the other dry ingredients. If you have access to a cement mixer, that is a good way to get the dry ingredients mixed together. Just dump them in and walk away for 15 minutes while it chugs away. Once water has been added to your thoroughly-mixed dry ingredients, you shouldn't let it sit, but get to work right away. I have used your same recipe with with vermiculte and it works just fine. I agree with Billie -- sounds like you may have made the recipe just too wet -- remember you should not be able to pour hypertufa, you have to tamp/press it into your molds. Sand will make your end product stronger, but it will also make it heavier. Don't forget to throw in a handful of fiberglass fibers to help with strength. These come from the masonry supplier, and are fairly inexpensive.

Have fun, you will get the feel of this, and if something breaks or doesn't do to suit you the first time not to worry -- we have all been there (... and more than once) :)