Assuming that uploadedBytes is changing during upload.

-> Call this script when you know that the upload starts:

var timecontroller = setInterval(function(){

    timeElapsed = (new Date()) - timeStarted; // Assuming that timeStarted is a Date Object

    uploadSpeed = uploadedBytes / (timeElapsed/1000); // Upload speed in second



    // `callback` is the function that shows the time to user.

    // The only argument is the number of remaining seconds. 

    callback((totalBytes - uploadedBytes) / uploadSpeed); 

}, 1000)

-> When the file was fully uploaded, clear interval timecontroller:

clearInterval(timecontroller)

Pay attention that timeStarted must be a Date object.

Tell me if its work.
Thanks to @Stefano Sanfilippo - I use some of his script.