That's a great tip that, which leaves me with 3 out of 4 uncracked/chipped. Oh yeah, is 3 hours a good enough rotation?
That's hard to say. It depends on the power of your UC, and other things. In general, trial-and-error is often the best guide.
I have a fairly powerful UC (intended for medical/dental offices for cleaning tools). The timer on it will only go to (I think) an hour and a half, but it's a completely different animal than, for example, a jewelry cleaner. (it also has a basket, which keeps the bottles off of the very bottom of the tank, and therefore gets the US energy to spread better). I'll often do 2 cycles for the full duration. If it's done and I'm too lazy to take it out, I might do another one. But, since it's big and can do more than all the juice I will ever make at one time, I've never tried to streamline the process.
If you're going to use the glass beakers, do yourself a favor and fill them with water, and then run them in the UC for an hour or so. That way, you can weed out a defective one without losing juice.
(Seriously, the ultrasonics will completely destroy a glass vessel with any kind of crack in it, and you might not see it when you put it in! And beakers are a bit more thin-walled than many glass jars).