Yes, they do. These are known as Egg Cycles. Some Pokemon are rather quick and some take a very long time.
For example, Magikarp will hatch after just 6 Egg Cycles, which is a low 1530 steps, and despite not being able to be in an Egg legitimately, legendaries have Egg Cycles coded, and some of them require 121 cycles, or 30855 steps.
*= at minimum. Certain happenings can reset the current Egg Cycle, making it take longer for Eggs to hatch.
Source: Bulbapedia / experience.