Back in the 90's I worked at a tier 1 (means the parts go from there to the car plant and are directly put on the vehicle) Toyota supplier and in the summer the day shift started at 5:30am to combat the heat. It would switch back to 7:30 in the fall. Thankfully I only had to do it for a couple weeks before being put on afternoon shift. Its really hard for an 18 yr old to get up and be at work by 5:30am!