CC1200DK: information needed on dal_send.pl TX API

In the scripts provided by TI for TX API on CC1200, there is a field for packet time interval as follow:

my $packetInterval = 1; # Second

but this local variable is not being used anywhere in this code. On the other hand there is another line for packet time interval as follow:

# Default packet interval for packet length of 30 bytes.
$dev->setDefaultPktInterval(4);

Now the question is how can I change the time interval between packets? if I supposed to use the "$dev->setDefaultPktInterval(4);" is there any reference correlating the number to the actual time interval?

Thanks