# code frag written in long hand for clarity (I hope)
my $delta_day;
my $now = time();
my $oldiptime = ---from your file --
(($now - $oldiptime) >= 86400) ? ($delta_day = 1) : ($delta_day = 0); 

##</code><code>##

# code fragment there's a use strict lusting above
if ( exists ($IP_LIST{$ip} ) {
  go check delta day and stuff
} else {
# sdd it 
  $IP_List{$ip} = $now;
}