How do you know how much studying is enough for your target score?

Well, my perfect plan of 3-4 months of studying for the GMAT over the summer/fall in order to apply R1 this year was ruined by some pretty bad medical news I got and a significant amount of time spent in the hospital and recovering from Chemo. Now I have less than two months to take the GMAT for R2 and I think it's highly unlikely I'll get to my target score in that time (700+), I'll probably end up having to apply R3 which I know hurts my chances significantly but it's the hand I was dealt so I'm going to do what I can with it.

I was hoping for some advice as to how intensively I need to prepare to get that 700. Like most people, I'm hurting in the quant section and I need to improve it substantially. It's not that I'm a doofus at math, but it never came easy for me. I got an A in Calc I but it took beating my head against a wall nightly for a few hours until I could understand the material. That was 6 years ago now and after going through the MGMAT math foundations it's clear that I've forgotten most of my math even going back to basic algebra/middle school stuff. I'm smart but by no means a genius, as you can tell from my crappy math abilities. I scored in the 97th percentile in CR and 80th percentile (yikes) in math in my SAT, although I didn't study intensively for that test, it should give an indication of my weakness.

So any guesses at what I'm in for? Do I need to set aside 30 hours a week for 3 months for any hopes at a 700+? Can I get by with 2-3 hours 6 days a week or less?

I'm honestly not too worried about the verbal section, I majored in the humanities at a top school and did well, that stuff always came much more naturally to me than STEM. I know I will have to put work into it but it's certainly within reach for me to reach my target score for that section, imo.

I appreciate any help anyone can offer, thanks.