If you're counting down the hours because you want a McChicken instead of a chicken biscuit from McDonald's, the accuracy of your countdown relies on when you can order through the drive-thru.
McDonald's is franchised, not company-owned. McDonald's maintains similar regulations for franchisees, including odd worker limitations, but allows moderate hours deviations.
USA Today has a relatively clear answer for when McDonald's begins serving lunch nationwide. In most U.S. areas, it's 10:30 to 11 a.m. Some sites start later on weekends, according to USA Today.