I'm used to working with dental grade algenate for everything, which can set in less that 2 minutes if room temp water is used. The reasoning that such a fast setting algenate is used is because of how common freakouts happen, even cutting off 5 minutes can can be the difference when it comes to a good vs a ruined cast because of facial movement or freaking out. Also why i use fast set plaster bandages, because when you put some salt in the water, the set time is cut in half.
Dental is faster setting, same level of detail, is stiffer but as pointed out, doesn't last long. But all my lifecasts go straight from the persons face to being prepped for casting, 10 minute wait at the most. If i plan on a wait, or need a specific casting material i use silicone. Not to mention, if you are making silicone prosthetics and the head becomes sulfur contaminated somehow you can make another one to the exact same dimensions since you still have the lifecast sitting around in workable condition. Some of the downfalls of dental is the fact that it requires much more water, and is constrantly "wet" which means your casting options are limited, but because of the extra stiffness the chance of seepage or collapse is greatly reduced