Totally depends on how fit you are! And I expect conditions on the day/s will make a big difference. (My opinions are of course subjective)
The middle section took me just over 6 hours back in May, conditions were good.
One way in 3 days is a relatively leisurely pace. (But don’t underestimate how many gates you’ll have to open and close!)
One way in 2 days is good going for a reasonably fit rider. (probably what I’d be aiming for, personally)
One way in 1 day is impressive.
So, both ways in 3 days is certainly doable, but not to be taken lightly. Or if you’re well prepared, it may be a piece of cake for you.
Bikepacking.com classes it as a 3-dayer in one direction. So might be worth looking at how they score other routes that you have done for comparison.