“How long does optic neuritis take to heal?”

varies
decreased vision typically comes back (maybe not fully) 4-6 weeks after IV steroids

Most people start to recover within two weeks and recover as much as they are likely to within six to 12 months. Most people's vision improves, but there can be lingering issues such as trouble with color vision for some people. The concern that I would have is, did you receive a diagnosis as to what the cause of the neuritis was? Has this problem been re-occurring or is this a first time situation? Are you still under the care of an eye doctor? Were you placed on steroid medications in order to reduce the inflammation, and have you properly used any medications prescribed? I would suggest that you follow up with your eye doctor, especially if you have any questions or you are concerned about anything related to your eyes or the neuritis. Good luck and best wishes.

Depends on severity. Normally you are on topical steroids and maybe even oral steroids for a few months

It depends on the cause. Often vision improves in a few weeks.