I would do it with a combination of variables and timers, so you do :
combo - variable for tracking which move of the combo you are on
on button pressed : start timer for 1 second, add 1 to combo
on timer ended : set combo to 0
/and for the animations
on button pressed :
if combo = 0, play attack anim 1
if combo = 1, play attack anim 2
if combo = 2, play attack anim 3