await只适用于承诺。您需要将setTimeout Package 在承诺中：

const waitFor = delay => new Promise(resolve => setTimeout(resolve, delay));

await waitFor(500);

setTimeout()不返回一个Promise，但是你可以像这样把它 Package 起来。我还稍微清理了一下你的代码的其余部分。

async function processMatchingSchools(customer_metafield_url) {
  for (const item of customer_metafield_url) {
    await new Promise(resolve => {
      setTimeout(resolve, 500)
    })

    const { data: { metafields } } = await axios.get(item)

    for ({ value, owner_id } of Object.values(metafields)) {
      if (value === schoolName) {
        id_for_each_student.push(`${shopifyAdmin}/customers/${owner_id}/metafields.json`)
      }
    }
  }

  console.log("Customer metafields to search", id_for_each_student)

  processOwnerIds(id_for_each_student)
}

setTimeout不返回承诺，因此无法进行await编辑。
您可以创建自己的基于承诺的setTimeout并使用它。

const setTimeoutPromise = timeout => new Promise(resolve => {        
  setTimeout(resolve, timeout);
});

await setTimeoutPromise(500);

创建一个sleep函数，返回一个可以使用的promise，如下所示：

const sleep = (milliseconds=500) => new Promise(resolve => setTimeout(resolve, milliseconds))

要在异步函数中使用它：

(async () => {
  console.log("function invoked...")
  await sleep(500)
  console.log("I got here about 500 milliseconds later")
})()

你需要创造新的承诺比如说

function delay(ms){
 return new Promise(resolve => setTimeout(resolve, ms))
}

然后在调用API之前在代码中使用它

...
await delay(500)
await axios.get(item).then((res) => {
...

我创建了setTimeout2函数，其工作原理与promise相同：

const setTimeout2 = (callback, ms) => {
  return new Promise(resolve => setTimeout(() => {
    callback();
    resolve();
  }, ms));
}

因此，总的来说（注意到setTimeout2变更）：

async function processMatchingSchools(customer_metafield_url) {
  for (const item of customer_metafield_url) {
    await setTimeout2(function(item) {
      axios.get(item).then((res) => {
        for (key in res.data.metafields) {
          if (res.data.metafields[key].value === schoolName) {
            id_for_each_student.push(shopifyAdmin + "/customers/" + res.data.metafields[key].owner_id + "/metafields.json")
          }
        }
      })
    }, 500)
  }
  console.log("Customer metafields to search", id_for_each_student)
  processOwnerIds(id_for_each_student)
}