Currently your code looks like this :

my ($sec,$min,$hour,$mday,$mon,$year,
     $wday,$yday,$isdst)=localtime(time);
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The time keyword returns an integer value of seconds since epoch... if you decrement that value before sending it to localtime you can return any date/time you want. I.e :

my $week_of_seconds = 60 * 60 * 24 * 7;

my $current_time = time();

my $week_ago = $current_time - $week_of_seconds;

my ($sec,$min,$hour,$mday,$mon,$year,
     $wday,$yday,$isdst)=localtime($week_ago);
[download]

The above isn't tested because I can't be bothered, the solution looks more or less like that, play around with it.