Display Seconds Count in HH:MM:SS format in SSRS 2008

Just use an expression that adds that number of seconds to a zero time value

=Format(DateAdd("s", Fields!TotalTime.Value, "00:00:00"), "HH:mm:ss")

If it is larger than 24 hours, then you can use the following formula that adds the days portion:

=IIF(Fields!TotalTime.Value < 86400, 
    Format(DateAdd("s", Fields!TotalTime.Value, "00:00:00"), "HH:mm:ss"), 
    Floor(Fields!TotalTime.Value / 86400) & " days, " & Format(DateAdd("s", Fields!TotalTime.Value, "00:00:00"), "HH:mm:ss"))

For HH:mm:ss format you can use this:

=Floor(Fields!TotalTime.Value / 3600) &":"& Format(DateAdd("s", Fields!TotalTime.Value, "00:00"), "mm:ss")

In this case, for example 90000sec will be displayed as: 25:00:00

For DD:HH:mm:ss format use this:

Floor(Fields!TotalTime.Value / 86400) &":"& Format(DateAdd("s", Fields!TotalTime.Value, "00:00:00"), "HH:mm:ss")

90000sec will be shown as: 1:01:00:00