Congratulations! It sounds like you are making progress.
7-10 minutes also sounds about right to me. If you experience discomfort during the fill you can lower the presure even more and the time to administer will take longer. Keep the bag only high enough so that if you cramp, it will not backflow into the bag.
I prefer the fluted douche nozzle to the straight rectal nozzle. It is easier to retain and the extra holes give a more even flow. The insertion depth is up to you but do not force it.
For the insertion of this or any nozzle you can easily determine the exact placement and insertion direction if you use a gloved finger to lubricate the inside surface of your anus. Do this immediately before inserting the nozzle and the finger will tell the brain where and what angle to use.
As to what position to use, I generally use either the left side or on my back. On the left side the initial inflow of water will flow downhill to fill the descending colon. Many people recommend starting on the left side then rolling on the back to fill the transverse colon, then the right side to fill the ascending colon. Starting on the right side, the water will have to climb uphill for a while. I find the knee-chest position to be awkward for me, but that is just my preference. About the only position which doesn't work for me is face down. For a good complete fill, I find the back works best for me.
Whatever position you choose, try for a complete fill. The quantity of water to achieve a complete fill varies for individual people and could be anywhere from 1.5 qt to over 4 qt. The correct amount for you is whenever your body tells you it is full and can't hold another ounce even after clamping the hose and resting for a while. I regularly take 4 qt, but I have been doing this for over 50 years. Don't force anything!
Disclaimer: I have zero medical training and this is not medical advice, only my own experience.