I came across this thread while searching for dry-times on pre-mixed thin-set. I signed up to give some feedback perspective. I realize the thread is old... but just wanted to share my opinion. I am technically a contractor since I have an A/C technician license... but I only got it so I could legally buy R12 and R22 freon myself because I'm a cheap bastard and do everything myself.
So here's my views of the pre-mixed thin-set. I reluctantly agree with a lot of the things that have been said. I'm not a pro. I'd say I'm a weekend warrior that does projects that keeps me occupied every day after work for years. I'm on my second home renovation. I renovated my home in Florida just prior to moving (only got to live in it for 6 months) before I moved for work and rented it out, and now I'm renovating this other house I just bought, and I'm about half-way into it.
Having tiled an ENTIRE 2,400 square foot home... bathrooms and large open areas using pre-mixed, I'd have to say that there are some definite "down-sides."
I learned the hard-way that the pre-mixed is NOT good for shower floors. I experienced this the hard way. I laid sheets of smooth stone on the shower floor using the pre-mixed. Within a month, the thinset had re-emulsified and the little stones were moving. I ended up not using the shower for two weeks, then loaded it up with grout, and poured tile sealer (1/16" thick) pool of it all over the floor while covering the drain. 1 year later, still good. If it happens again, I'll have to send someone out to pull it all up and use real mortar.
For the most part, the thin-set has been pretty decent when laying the tile. When I had 12x24" tiles, it wasn't so bad, but when I stepped up to 18" tiles... I experienced the problem many of you guys are talking about. Literally took two weeks for the tiles to fully dry. I think in effect, the concrete below it had to "suck-up" the moisture. I'm reminded of one time when I had laid the tile where the fridge would go, and I rolled the fridge back into that location after a week and the tiles literally buckled and snapped under the fridge. I had to pull out my jack hammer again, and relay all new tile. The pre-mixed thinset was still "fresh" like it hadn't even dried slightly.
When it does dry, it's rock-hard... like the old thin set that I've been jack hammering up. I've since used it in the dining room, kitchen, and breakfast area of this new house. I also used it in a bathroom floor, and it's been good there (no shower floor).
When I do the main area of the house (this new house is 2,800 square feet), I'll probably used mixed.
The ONLY benefit that I can say exists from the pre-mixed... is if you are a home owner when Tulsa said it's for "HOs" (unless there are a special kind of escorts in Tulsa). It's useful to me because I may only have time to lay 4-5 rows of tile one night... on say, Tuesday, after work. Even on the weekends with family and kids, I don't get the opportunity to spend more than ~4 hours at a time working on the house.
So, hopefully that was helpful to anyone else that finds this thread.
Just DON'T use it on shower floors!!!