If you are in Rochester, NY you are lucky to have a great resource, Bill Valavanis and the International Bonsai Arboretum. Do call, visit if you can Bill has been doing bonsai for maybe 50 years and has tremendous knowledge.
The Encore azaleas pretty much can be treated as Kurume Azalea. The second bloom in autumn only comes on older plants that have not been pruned too late in spring. If you leave them grow out and get "weedy" they will bloom twice, but they have a tendency to loose their bonsai shape. If you prune them to be in "bonsai shape" you rarely get the second bloom, because the growing tips with future buds have been removed.
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@Paradox - sorry Sandy, I needed to correct the spelling of Kurume, easy mistake to make)
The difference between Satsuki and Kurume azalea is mainly that in spring, Kurume will tend to wake up, and then bloom fairly quickly after breaking dormancy. Satsuki azalea, will wake up in spring, grow for a while, then bloom, in zone 6b or 7a starting in May or early June, finishing flowering about 4 weeks after starting. There are hybrids between the two groups and their behavior is intermediate. All Kurume and Satsuki are evergreen azaleas with relatively small thin leaves (when compared to Rhododendrons) which makes both groups nearly ideal for use as flowering bonsai.
So if you like the flowers of your Encore Azalea, great, you can treat it like a Kurume azalea in terms of when to prune it. Rick Garcia has a great book on how to grow and train Satsuki azalea, with some notes on Kurume. Almost all the horticultural information as bonsai in Rick's book about Satsuki azalea applies to Kurume except for the detail about blooming as they come out of dormancy.
I could go through the details, but if you can visit Bill Valavanis over at International Bonsai Arboretum, he will likely have Rick Garcia's book in stock and have his own take to add on azaleas.
