I was gonna say I never have less than 15 at any point. 
So 75 is not low. Mine have been as high as 49. But I don’t put in 3 unless I have to for time to finish reasons.
I usually put one in and then go do other things in the area. When it activates I come back you can always get back before the Blood Maiden comes out of her egg…and I am fairly sure the buff stays, I mean I don’t go to the other section of helltides or anything.