What constitutes first, second, and third work shifts?

In the workplace, there are different types of work shifts, some lasting up to 24 hours. These shifts are typically 8 hours long and are known as 1st, 2nd, and 3rd shift. The 1st shift is usually from 9 a.m. to 5 p.m., the 2nd shift from 5 p.m. to 1 a.m., and the 3rd shift from 12 a.m. to 8 a.m.