How long does it take to build a CMS?

I googled this before but I thought I would ask for more of real time update from developers. E.g i'm building with django at the moment i'm sure i've already build abot 50% but within a few days.

So if i was to take on a custom cms for e.g company how long would I need to quote to build a fully functional one? six weeks? 3 Months?