你需要将值拆分：，在通过模运算符运行第一个值后重建它。试试这个：

You need to split the value by :, the rebuild it after running the first value through the modulo operator. Try this:

var offTime = "17:25:11".split(':');
offTime[0] = offTime[0] % 12;
var output = offTime.join(':');

alert(output);