在倒计时结束前一分钟显示提示框

I am working on an online quiz module where the quiz auto submits after 30 mins. Now I want to show an alert box where in the student gets notified "1 minute left to finish quiz" on the 29th Minute. I am unable to figure out how to implement this. I have my code as shown below for this.I am working on an online quiz module where the