Hormone level was 3600 then dropped to 2400 2 days later how long til they are zero?

Depends: I am assuming you are talking about HCG levels? Also is this drop related to a miscarriage? Most will return to zero within a few weeks. If levels remain elevated, it would be concern for retained products of conception or the possibility of something known as trophoblastic disease. Your provider should monitor your levels if there is any concern. Hope this helps