Not sure if I understand what you're trying to accomplish here... Is there a concern that the script can be started by multiple users simultaneously? Or do you simply need a delay between successive requests made by the same process?
If latter is the case, you have your answer already - sleep().

If not, and you need logic to gate requests from multiple instances of the same script, you can use a lock file.

use Fcntl ':flock';
my $file = 'file.lck';
open my $lfh, ">>$file" or die "Can't access $file : $!\n";
if (flock $lfh, LOCK_EX){
  sleep 1 while (time - (stat $file)[9] < 1);
  #
  # Send your Amazon requests here
  #
  utime time, time, $file;
}else{
  print "Can't lock $file: $!";
}
close $lfh;
[download]

The code is untested and may not work if you simply cut and paste it. It should, however, give you an idea of how to approach the problem.

--perlplexer