I've always taken Tom's advice:
"I like this blend best when the roast is stopped while second crack is
extremely rapid, and shows no sign of slowing down. But this may be too
acidic for some. It works quite well roasted to the point where 2nd
crack slows, but has not yet ended. Roast to the absolute end of 2nd
crack, and you might as well be drinking Robusta. I believe strongly in
a 24-36 hour resting period before use for espresso extraction! But it
wont kill you to use it sooner... "
I find this works very well, and Monkey is one of my favorite espressi.
I also really love Sumatrans and Sulawesi and it's true that Monkey is
"sharper" than either (I'm drinking a double shot of Sulawesi Toraja as
I type this)...
Oh, btw, what roaster are you using?