This value reflects the estimated number of seconds of transfer left. It is based on the amount of data transferred and the average data transfer rate. Because data transfer rates may vary the SecondsLeft property is an estimate - it may increase or decrease as network conditions change.

If the sum of ElapsedSeconds and SecondsLeft exceeds Server.ScriptTimeOut you may wish to inform the client that their transfer is likely to time out.

ElapsedSeconds property.