How many days ork 90 hours is equal too depends on what type of flying you are doing...doing short haul turnarounds you'd likely have to work every day of the month to get that...typically it would be between 8-12 days off now a month and over 300 hours away from homebase.
It's the times zones and back of the clock flying that wears you out. No way you can sustain a long haul multiple time zone type of lfying at 8 days off a month..you simply need 12-15 at least to recover.