Somewhere Googlie pondered whether it would be possible to rushbuild the MCC the turn we research DocIni, ie in four years.
I haven't done any tests, but if you start from the following facts:
a) Using the two artifacts, we still need 200 minerals.
b) Our total factional mineral production (support not included) is 45 minerals per year.
So even if all bases started constructing crawlers next year, which I assume cannot be done, we'd still need at least five turns (5*45>200).