One guide, https://support.cambridgeenglish.org/hc/en-gb/articles/202838506-Guided-learning-hours

Common European Framework Guided Learning Hours (from beginner level)

CEFR Level Cambridge English Exam Number of Hours (approximate)

C2 Cambridge English: Proficiency (CPE) 1,000—1,200

C1 Cambridge English: Advanced (CAE) 700—800

B2 Cambridge English: First (FCE) 500—600

B1 Cambridge English: Preliminary (PET) 350—400

A2 Cambridge English: Key (KET) 180—200

I'm not sure how C2 compares to "90% of native," because people can be very skillful in reading, writing, and understanding English and still be instantly identifiable as not being native speakers, but I suspect "90% of native" means C1 or C2 and that about 1,000 "guided learning hours" is realistic.

I personally have probably spent about 500-600 "guided learning hours" on Spanish and I'm somewhere in B2 but maybe near the higher end, according to the Cervantes Institute's quick placement test, so that matches up pretty well.