动画持续时间 - Animate.css

Question

我无法操纵使用Animate.css进行动画处理的元素的animation-duration。我在一个形状像箭头的跨度上使用flash动画，但它的速度太快了。所以，如果可能的话，我想放慢速度。这是我的代码：

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* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Roboto', sans-serif;
  overflow-x: hidden;
  color: #333;
}

header {
  position: relative;
  text-align: center;
  height: 100vh;
  background: linear-gradient(to right, #69bcf4, #30cc8b);
  color: #fff;
}

header h1 {
  padding-top: calc(50vh - 133px);
  font-size: 7em;
  font-weight: 100;
}

header h2 {
  font-size: 2em;
}

header span {
  position: absolute;
  margin: auto;
  right: 0;
  left: 0;
  bottom: 30px;
  height: 4px;
  width: 4px;
  border-radius: 2px;
  background: #fff;
  animation-duration: 5s;
  animation-iteration-count: infinite;
}

header span::before,
header span::after {
  position: absolute;
  top: -23px;
  content: "";
  height: 30px;
  width: 4px;
  border-radius: 2px;
  background: #fff;
}

header span::before {
  left: -10px;
  transform: rotate(-45deg);
}

header span::after {
  right: -10px;
  transform: rotate(45deg);
}

.scroll-animations {
  display: flex;
  
}

.scroll-animations div {
  flex: 1;
  padding: 20px;
  text-align: center;
}

.scroll-animations div span {
  font-size: 4em;
}

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<link href="https://cdnjs.cloudflare.com/ajax/libs/animate.css/3.5.2/animate.min.css" rel="stylesheet"/>
<div class="wrapper">
  <header>
    <h1 class="animated bounceInDown">Lorem Ipsum</h1>
    <h2 class="animated bounceInDown">lorem ipsum dolor ip semet</h2>
      <span class="animated flash"></span>
  </header>
  <div class="scroll-animations">
    <div>
      <span>&#9742;</span>
      <h3>Number One</h3>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum quis lacinia est. Nulla malesuada massa orci, vitae placerat lorem pharetra a.</p>
    </div>
    <div>
      <span>&#9835;</span>
      <h3>Number Two</h3>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum quis lacinia est. Nulla malesuada massa orci, vitae placerat lorem pharetra a.</p>
    </div>
    <div>
      <span>&#9730;</span>
      <h3>Number Three</h3>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum quis lacinia est. Nulla malesuada massa orci, vitae placerat lorem pharetra a.</p>
    </div>
  </div>
</div>

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