i would say 30 mins and see from there ( pot full of water with tin foil over it, and just put the end of the wood you want to bend in the water it wont hurt it. bring it to a boil/steam the living hell out of it.. should get the job done.. its pretty thin after all. ). also you will want to get some kind of strap to put on the back side of the wood when you bend it.. that will help keep it from pulling a fiber. heck you could even cut a soda can open if that is all you had.
( also, this should be real easy to do with 99 percent success rate compared to a recurve into a wood self bow.. because the degree i had to bend in the curve was pretty extreme... heh. )
you can use any kind of metal that is thin. tin, etc..
you do not have to use such but i would recommend it if you can find something.
i hate to say this but this gonna be trial and error. but i think its worth investigating.
also be sure to bend the wood with the edge grain to the side. so look for the lines.. not the grain pattern.. i hope that makes sense.
i still plan on building you some arms this winter out of laminated bamboo too..
chris.