Delay a Code Block

#1. First, you need to find Code Block ID.
In my example, it is: #block-yui_3_17_2_1_1729047562015_20924

#2. Next, use this code to Custom CSS box

#block-yui_3_17_2_1_1729047562015_20924 {
  opacity: 0;
  visibility: hidden;
  transition: opacity 1s ease-in-out;
  animation: showElement 0s 4s forwards;
}

@keyframes showElement {
  to {
    opacity: 1;
    visibility: visible;
  }
}