如何在 vu-countdown 中使用变量作为剩余时间？

项目中有个倒计时的需求，之前用 vue-countdown 做过获取验证码的倒计时，但是时间是写死的，现在想再用这个来做，但是把时间设置为变量之后倒计时不会发生变化，代码如下：

<vue-countdown :time="countDown" :interval="1000" :auto-start="true" ref="countdown" class="count-down"> <template slot-scope="props">{{ props.days }}天{{ props.hours }}时{{ props.minutes }}分{{ props.seconds }}秒</template> </vue-countdown> <script> import axios from 'axios' import VueCountdown from '@xkeshi/vue-countdown' export default { components: { VueCountdown }, data () { return { countDown: 0 } }, created: function () { axios({ method: 'GET', url: 'http://a.b.c', withCredentials: true, headers: {'lang': 'zh', 'token': '', 'os': 'web', 'version': '1.0.0', 'time': ''} }).then((response) => { let respOnseData= response.data.data let respOnseStatus= response.data.code this.needNum = responseData.needNum this.timeLeft = responseData.timeLeft if (respOnseStatus== 200) { this.payStatus = true let now = new Date() let timer = (this.timeLeft + 0) * 1000 let setNow = new Date(now.getTime() + timer) this.countDown = setNow - now this.$refs.countdown.init() this.$refs.countdown.start() } else if (respOnseStatus== 100) { this.payStatus = false } else if (respOnseStatus== 101) { } console.log(responseData) }).catch((ex) => { console.log(ex) }) } } </script> 

在 vue-countdown 的文档里也没看到相关的描述，如果要用它实现的话要怎么做呢？