From what I gather you're trying to time your sprites in a way that the feet don't "slide" along the ground?
You'll need to keep track of the time passed between frames(delta)
Delta can be calculated by subtracting the current system time of the previous frame from the current system time of the current frame.
Each frame in the animation will cover a certain range 0-25 ms, 26 -50 ms. 50 - 60 ms, ect.. You can either assume the time is uniform or assign different lengths to each frame, but keep track of the total time the animation takes to play out. In this case 60 ms (totalAnimationTime).
1. Each time the sprite is updated pass in the frame delta. Keep track of the total delta time the sprite has been in the animation(deltaTotal).
2. Find the local delta (how far you're into the animation loop. (localDelta = deltaTotal % totalAnimationTime ) modulo finds the remainder.
3. If local delta is 0-25 ms render the first frame. 26-50 render the second, 50-60 ms the third, ect.