How to set the time interval for each loop of css3 animate animation

.item{
  webkit-animation: revolving 4s 0s infinite;
  animation: revolving 4s 0s infinite;
}
@-webkit-keyframes revolving{
  0,75%{
    -webkit-transform: perspective(700px) rotateX(90deg);
  }
  87.5%{
    -webkit-transform: perspective(700px) rotateX(0deg);
  }
  100%{
    -webkit-transform: perspective(700px) rotateX(-90deg);
  }
}

Set the total animation to 4 seconds, then the first 75%, which is 3 seconds, does not change (0-75%), and the next 25%, which is 1 second, can be animated.

For specific democan, see demo