How long do the cognitive and neurological symptoms of b12 deficiency take to heal after correction?

Depends on: Your age, how long you've had low B12 and how low it got. I usually try to keep the level above 450 for the first year and above 350 thereafter. In older people we tend to see incomplete recovery. Balance if impaired with eyes closed should start to improve with 6-9 months of therapy. Cognitive slowing can improve sooner. Some people report improved thinking within a week.