A neighbor bought two last year but they were a size smaller. The battery charger runs on 220 volts so a charge only takes 8 minutes. With three batteries in a rotation it won't be a problem keeping one drone in the air. We put a hose reel and a 120 volt pump on the tender to fill the drone instead of using gravity so down time should be less than 60 seconds. Moving the tender every other time or so to stay close to where the drone is working will also eliminate the dead time flying back to get tendered. If we can get anything close to 200 acres a day we'll be very happy. 
You mentioned charging the batteries in one while the other is flying; you don't charge the batteries in the drone. They lift out and you replace with a charged battery in about 10 seconds. Isn't even anything to hook up, just drop the battery in an off it goes. Like I said, we expect down time to be around 60 seconds from the time the drone lands, you fill the tank and switch a battery and the drone takes off again.