How long to run? That all depends on the ambient temperature. In hot weather it should take a shorter amount of time than cooler weather, as condensation will build up quicker. I have not personally worked on a CX-5's A/C system, but all vehicles I have worked on has the drain (not a plug, but a hose) on the passenger firewall. Once you find it, an unbent clothes hanger poked into it should clear it.
