A simple way to calculate the time is to use something like
long seconds = timeInMilliSeconds / 1000;
long minutes = seconds / 60;
long hours = minutes / 60;
long days = hours / 24;
String time = days + ":" + hours % 24 + ":" + minutes % 60 + ":" + seconds % 60;
This will work if you have more than 28 days, but not if you have a negative time.