I didn't notice, but is this a new facility? If so then the manufacturer of the generator should be responsible for the test. If it is an existing facility, then you should still contact the company that manufactured the generator and get their input about load testing. The customer that owns the generator should have input on the testing as well. But it all boils down to bringing in an external "load bank" that will be hooked up at the generator on the load side of the main. Usually the generator people do not want to mess with the wiring at the ATS unless it is their equipment. Now some facilities will let you use the "building load" for test purposes., but usually not if they are occupying the building. I have also seen load tests that use a combination of existing building load and the load from an external "load bank", but that requires an exact knowlege of what the building load exactly is so that the added load from the load bank does not overload the generators. As far as duration...I have seen load test take as little as an hour, and some up to 4 hours. Usually it is 2 hours on existing building load and 2 hours on 100% load throught the external load bank.