This method returns the estimated remaining time for the upload, measured in seconds. This information can be used for custom upload progress indicators.

The estimated remaining time is calculated dynamically. For example, if the first 10 KB of 100 KB takes 5 seconds to transfer, the estimated remaining time is (100K/10K) * 5 - 5; if the next 10KB takes 10 seconds to transfer, the estimated remaining time is (100K/20K) * (10+5) - (10+5).