A stubborn color correction in my Seattle chair took me 8 hours to finally get right.
The client had a base of box black dye over old highlights, and removing enough pigment to achieve her desired cool ash brown without frying her hair was a marathon of careful olaplex treatments and timed applications that I thought would take maybe three.
Bleach washes can be so unpredictable on different hair types though. Seen it turn some people's ends to straw in one go. Maybe a test strand is a good idea before going all in.