Help please? what is the duration of illness for meningococcal meningitis?

Less than a week: Once diagnosis of Meningococcal meningitis is established and proper treatment is rendered, recovery is pretty fast.

Varies: I have seen it go from first known symptom to death within 24 hours. I've also seen it be diagnosed from the rash in the first 8 hours, get treated and cured within a week. A lot depends on the quality of the immune system response of the infected person and their access to medical care.