convert seconds into dd:hh:mm:ss

Here's an example of an expression that converts an integer (the number of seconds) into a more readable format. Please replace <seconds> with the variable storing the number of seconds:

FormatBoolean(<seconds>/86400>1, Trunc(<seconds>/86400)+"d ","") + FormatBoolean(<seconds>/3600>1,
Hour(AddSeconds(NullDate(),<seconds>))+"h ","") + FormatBoolean(<seconds>/60>1, Minute(AddSeconds(NullDate(), <seconds>)) +"m ","") +
Mod(<seconds>,60) +"s"

Note: There are of course a lot of ways to do this formatting. This one uses a single inline expression to make it easier to apply the expression in your screen (ex. list records cells). It also uses the FormatBoolean function to prevent showing non meaningful parts of the "readable format" (ex. if you have 63 seconds in your <seconds> variable this expression will return "1m 3s" instead of "0d 0h 1m 3s)
In a .NET XIF, you can easily convert seconds to Time.

public void MssSecondsToTime(decimal sss, out DateTime sst) {
    sst = new DateTime( 1900, 1, 1, 0, 0, 0 ).AddSeconds( (double)sss );
} // MssSecondsToTime