life.js

var fs = require('fs');

function writeTime(){
    var lifedata;
    var filename = './life.json';
    fs.readFile(filename, 'utf8', function (err, data) {
        if (err) throw err;
        lifedata = JSON.parse(data);
        doWrite();
    });
    
    function doWrite() {
        var d = new Date();
        lifedata.time = d.getTime();
        fs.writeFile(filename, JSON.stringify(lifedata, null, 4), function(err) {
            if(err) {
                console.log(err);
            } else {
                console.log("written");
            }
        });
    }
}

setInterval(writeTime, 120000);