The average (not the processing time) processing time for applicants from Nigeria is 4months but I know of people who had their visa two months after applying (including the medicals). I also applied last week inAugust and still hoping to hear from the embassy as regards the medical schedule. However, you may want to have alternative plans like calling your institution and finding out the last acceptable day for registration and worse case scenario, have your admission deferred till September (let's hope it won't come down to that).
Fingers crossed my friend while we watch and pray.
All da best