One and a half days.
Visit SFWoA, get there as they open, you get on most of the rides, leave there at 2pm and drive to CP, arriving at about 4pm for the twilight rate.
They have 2 for 1 coupons in the Cedar Point book for the twilight rate, so order it online before you go. This makes your first day into the park super cheap.
Now, as you enter the park, buy your ticket for the next day so you have it.
Go on some flat rides, TP will be about a 30 minute wait, MF will be 2 hours, do this last.
The next day, be at the Marina gate early, like 08:30am, and sit there, long line forms. Gate opens, and you RUN to MF and get your 2 rides, queue will fill up, it's over, no more MF rides, then see the rest of the park. I am talking summer time, if you go in May/June, you'll get more rides. Don't go in August, park is super packed even on the weekdays.