3" seems pretty thick, but I've seen recommendations for min. of 2.5". I'm doing the same size, but was going to try 2", with some nylon fiber for support.

No one can answer your question without seeing the piece in person. It shouldn't take longer than a poured basement and it did. FYI, the hypertufa is curing not drying. Sounds like you are having fun!!!

Yes, I am having fun. Thanks. Basically just seeking opinions since no way are you gonna see this in person. Sorry for the misuse of drying and not curing. I will be careful in a future post.

Here is a link that might be useful: The Hypertufa Gardener

Why do you keep putting a link to Mike's web site in your posts?

I don't have a link to Mike's website in my post?

I have a link to mine, though. But if you visited and thought it was his, I am profoundly flattered.

Ahhh, thought it was Mike's. So why do you keep putting a link to your web site on all your new posts?

Why do you object? I am asked for that info, as an option, and I provided it.

I don't see a further need to discuss.

It's not asking for a link to your personal web site. It's a place to post a link to something that's relevant in your post like a product or tool or picture or an article.

But anyway, my questions: Do you think this is a typical dry time for a piece that large? will I need to worry about structural integrity? (It is reinforced inside the 3inch walls and bottom with hardware cloth.)
The longer you allow cement to cure , the stronger it gets. Using the word dry will only confuse people who are just learning the process.
I think it is not unusual to have a long dry time on a piece that large. It may also depend on how wet the hypertufa was when you put in the mold.

looks lovely with the different textured alpines growing in it

Thanks, and all of those were the tiny 3" pots this spring. Look how nicely they've grown! I will be making more of these large troughs because they really behave well for the plants. I have this wrapped in bird netting over the winter because the squirrels like to dig in it. >sigh More pictures of this big trough at my site.

Here is a link that might be useful: The Hypertufa Gardener

I often made troughs with 3" sides and bottoms, and they seemed to cure just as well as others, maybe better. It actually helps them to cure if you wet them thoroughly maybe every day while they are curing. Concrete cures better when kept damp.

I love your trough! What did you use as a form when you were making it?

We just built a box with screwed-in sides and bottom so it could be taken apart. Then we balanced it on large boards to carry it. Super heavy. I have some explanation on the blog. Lots of photos.

Im curious how much that triugh weighed when it dried?

I am not sure how much it weighed. Had to be moved by my son and son-in-law who struggled. Possibly over 100lbs. Now that it is full of soil and plants, I can't even consider moving it. But I LOVE it. I made a quickie film for a video into on YouTube.