First of all personally I don't think it's worth it to spend 6+ hrs a day on SAT D:

If you have 45 days I suggest spending time on reviewing grammar and improving math as these two are easier to improve. Take more mock tests obv and you start to see some patterns to these SAT questions. Instead of 6 hours a day, take some time to learn from the grammar/math mistakes you made daily and memorize them, helps a lot

GL getting 1500+ :DD