I don’t think studying for 10 hours straight per day is a realistic goal. Especially not for someone with a focus disorder and no stimulants – not that the stimulants will magically fix it, but not having them won’t help.
I think you need a study plan that has more variety and built in breaks. There are real limits to what the human brain can absorb, process and, retain in a given amount of time.
Give yourself built in breaks, add some variation by testing yourself and breaking up the material. Study for a bit, do something low stakes or relaxing if you can and then do more study. Try to cycle between learning/cramming and other activities throughout the day. Your brain (and everyone else) has limits, work with them for best results, not against them.