user_time = 1407805878;
var sse = new EventSource('server.php?user_time='+user_time);
sse.addEventListener('message',function(e){
    var data = e.data;
    var obj = JSON.parse(data);
    // here I have updated user_time from responce
    user_time = obj['time'];
    console.log(obj);
},false);

user_time = 1407805878;
var sse = new EventSource('server.php?user_time='+user_time);
sse.addEventListener('message',function(e){
    var data = e.data;
    var obj = JSON.parse(data);

    // here I tried to update URLe
    sse.url = 'server.php?user_time='+obj['time']
    user_time = obj['time'];

    console.log(obj);
},false);