With a 77" bow that would be 102 minutes! 2min * (77"/ 1,5") = 102.
Most of the time i end up spendin 20-40 minutes heat treating a bow. 40 minutes if its as thick as this one. Basically you just want to get the wood hot through out. I share the same opinion about heat treating as Steve Gardner (Badger) for example, you just need to get the wood hot, quite nothing else matters. What i've heard Steve likes to move the heat gun all the time heating the whole limb at a time. I have my heat gun stationary on a handy wooden stand. Sometimes i have two heat guns which makes the process faster. While you don't need that black or brown color, just get the wood so hot through out that you cant comfortably touch the back of the bow, i don't care too much if i happen to scorch a little. Its more cosmetic in my opinion as anything else, maybe a even light brown color would be the most beautiful for my eye. Elm becomes really beautiful after heat treating and finish.
Here is a picture of one of my elm flight bow, quite dark heat treatment and tung oil. The other bow is a dull looking norwegian maple longbow. You can see the difference of color between these two woods .
Oh and about adding poundage, i think if you do the heat treatment early to a fresh wood, you get the most out of heat treating. It might just be you don't spend up enough time heat treating. Enough long is when you get as bored about it as me and make a wooden stand for your heat gun.
