You could be pouring your duplicate models in about 15 min. You could use regular alginate in stock trays if you soak the casts first in Saturated Calcium Sulfate Dihydrate Solution. Get them nice and saturated and blow off the excess water before taking the impression. You have to pour them immediately within 5 minutes. Up to 30 min if wrapped with a soaking wet paper towel. I don't know if I would use the technique for fabrication of cast metal frameworks though. For those I would use irreversible duplicating silicone if you are looking for fast (about 45 min) I just use reversible hydrocolloid because I prefer to reduce my carbon footprint as much as possible. But the alginate method does work well for full/partial dentures.
One more important thing about duplicating. I like to block out any undercuts that are not critical to the fit of the prosthesis, prior to duplicating. So if you have a Kennedy Class 1 bilateral distal extension rpd that you will be fabricating for replacing the molars, I would block out the buccals and facials of everything anterior to the second bicuspids, or whatever teeth you are planning to use as retentive abutments. I like using biteblock wax for blocking out because I have an old trusty Hanau hot water bath that keeps the wax very pliable. I can block out in seconds. Blocking out non-critical areas reduces the undercuts, leading to easier retrieval of the master model and lessens my chance of having a distorted duplicate model. I would definitely recommend blocking out the vestibular roll area of the cast for RPD's and any non-critical areas if you plan to use the duplicated casts to process acrylic to. Obviously, if you are going to duplicate a cast for full dentures, first place your post-palatal seal, but don't block out the vestibular roll. Just make sure to blow off the excess water before you duplicate. I can't stress the importance of that step.
