As far as I know you can call functions in animation frames.
Have a combo_window bool somewhere. For example, if kick has 17 frames, call function that will set combo_window to true at frame 10 and to false at frame 15.
When user press a key for different kick, if it's in combo chain check if combo_window is true. If it's true continue comco chain, if it's not execute it as seperate kick.
Not tested, but that's how I would set it up.