10 mg bumps that's pretty weak even for pure stuff, 20-25 mg seems more like it.
A better question is how much time to leave in between the bumps because you are 'not feeling it yet'. I have overdone it quite a few times because of that, although thats when I had more experience and didn't care about too much :D
Take about 15 minutes to see what it does to you, perhaps after the first bump assume you won't get floored but after the second definitely see where it lands you and wait a tad longer.
Of course, it depends on how far you care to go - it's much better without any alcohol, also remove distracting noise or people or too much light, although having someone silently chilling out with you is okay, especially when participating.