element-plus/docs/examples/date-picker/default-time.vue

<template>
  <div class="demo-date-picker">
    <div class="block">
      <p>Component value：{{ value }}</p>
      <el-date-picker
        v-model="value"
        type="daterange"
        start-placeholder="Start date"
        end-placeholder="End date"
        :default-time="defaultTime"
      ></el-date-picker>
    </div>
  </div>
</template>

<script lang="ts">
import { defineComponent, ref } from 'vue'

export default defineComponent({
  setup() {
    const value = ref('')
    const defaultTime = ref([
      new Date(2000, 1, 1, 0, 0, 0),
      new Date(2000, 2, 1, 23, 59, 59),
    ]) // '00:00:00', '23:59:59'

    return {
      value,
      defaultTime,
    }
  },
})
</script>