I mixed the directions Lush provided (which actually differed from their video tutorials) with the one Curly Nikki suggests and here's what happened...
Lush Henna comes in a solid block so I began to grate it (their directions in the video) with a cheese grater but got tired and was taking too long so I started chopping it like chocolate (again their instructions in their video but the ones on the actual bar required a double boiler :/ ). I began to add my hot green tea and honey (as suggested by CN) and didn't like the consistency the chopping was giving me so back to grating I went.
I let it sit on my hair for a little over 6 hours and then used my shower hose to rinse most of the henna out before I got back in the shower to condition the rest out. Unfortunately the Lush henna has a very sandy consistency and rinsing the stuff out was more like rinsing muddy sand out my hair. It seemed like it was never ending!
I finally stopped rinsing after my hot water turned cold, got out blot-dried my hair with a t-shirt (produces less frizz than a towel), applied my own Deep Conditioner (Coconut Oil, Olive Oil, and Honey), put on a plastic cap and wrapped it up with a t-shirt (to help keep the heat in) and took a nap.