After 3 hours in the form, I got impatient and wanted to see if it took any backset. I got it off the form and it did take some, but not as much as I would have liked.
I proceeded to lay out the design on the back and reduce the material to almost the lines, leaving the handle blocky. I have also marked off 1/2 inch thickness from back towards the belly and hope to get that excess material off this evening. I have never floor tillered elm, but the few osage and hickory bows I have attempted, a thickness of about 0.4 inches got the weight close to where I wanted it. I figured 0.5 inches would get the limbs bending some (with a little to play with) and I might give the steam chamber another go this weekend at a slightly thicker limb than final dimensions.
Torges advocated steaming and forming before you tiller the bow. Whatever happens, I know I can use the heat gun to try and correct any other issues later on.
If nothing else good came out of the steaming today, at least it sped up the drying process! HA!