The shell is not the best tool for date/time arithmetic. Assuming you have perl...
Code:
#!/usr/bin/ksh
touch -t $(sed 's/\(..\)$/.\1/' payt_date.dat) payt_date.dat
perl -e '
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
$atime,$mtime,$ctime,$blksize,$blocks)=stat("payt_date.dat");
($ss,$mm,$hh,$DD,$MM,$YY)=localtime($mtime+600);
printf "%04d%02d%02d%02d%02d%2d\n",$YY+1900,$MM+1,$DD,$hh,$mm,$ss;
' > payt_date_plus_ten.dat
cat payt_date_plus_ten.dat
20031007202031
