Thanks a lot.

Below code worked:

string Format = "+%t,f3,f1,f2,f4,f6,f5";

function main()
{
int Records = dataParse(1,Format,InName);
printf("n%d lines read",Records);
dataSort(1);
int i;
for(i=0; i<Records; i++)
dataSet(1,i,0,(dataVar(1,i,0) - 25569.)*(24.*60.*60.));

dataSaveCSV (1,"%d/%m/%Y,f3,f1,f2,f4,f6,f5","check.csv");
if(Records) dataSave(1,OutName);
}