You'll need to do that yourself. Typically footsteps are called as the actual foot of the prefab touches the ground, and not just on a looping time system, since everyone's animations and ground detections and ground types and all that stuff is different. A simple looping time system can work in some cases, but it's not that bad to tie the sounds to he animation - AnimationEvents make this pretty easy to do now.
This tutorial is pretty comprehensive: https://www.youtube.com/watch?v=IK5hATN-rBw