There are many ways round this without having to resort to a sleep - the most obvious being Time::HiRes, which (although system-dependant) will give you a much higher resolution than time().

Another way is to add a counter variable, something like (untested)...

my %idcount;
my @ids;
for (0..5){
  my $t=time(); 
  push @ids, $t."-".++$idcount{$t};
}
[download]

...resulting in "12345678-1","12345678-2" etc.

Cheers, Ben.