I just tried to execute this on some steps in my front drive. Even doing what Builder93 suggested it could be difficult to remove forms. The bevel is probably a great idea and 1x1 or 2x2 will be easier. I cut down 2x4' to make the cantilever forms. The boards were run through a drum sander then a jointer. Final dimension was 1-3/8" x 2.5" or so. They were all smooth and straight and I still couldn't get them out a month after the concrete was done. Since it's been raining so much I just stopped trying altogether. I don't want to chip the concrete.
Also of note. The contractor really didn't want to do this. He suggested some pool forming product that is foam and can be easily removed. Unfortunately that product looked like the edge of a pool to me and not a modern cantilever step. I also tried to get them to apply vaseline (recommended by landscape architect I contacted) and they really didn't put enough on there to lubricate anything but their hands. Finally the idiots toe-nailed the inside corners of the cantilever forms to keep them flat making it pretty damn hard to pop the sides off first. Keep in mind the guys building concrete forms are not carpenters.
I think I'm going to play the patience game and let the wood continue to dry naturally before I try and pry them out again.