use strict;
use warnings;

my $logStr = <<LOG;
20:21:09:366500902 94.102.XX.XX > 63.77.X.X 65
20:21:09:484721194 63.77.X.X > 94.102.XX.XX 140
20:21:10:367148691 94.102.XX.XX > 81.192.X.X 65
20:21:10:432251992 81.192.X.X > 94.102.XX.XX 140
20:21:11:367836444 94.102.XX.XX > 103.229.X.X 65
20:21:11:665980944 103.229.X.X > 94.102.XX.XX 149
20:21:12:368606359 94.102.XX.XX > 69.33.X.X 65
20:21:12:588588107 69.33.X.X > 94.102.XX.XX 149
20:21:13:369344850 94.102.XX.XX > 85.32.X.X 65
20:21:13:396157789 85.32.X.X > 94.102.XX.XX 150
20:21:14:369986605 94.102.XX.XX > 4.28.X.X 65
20:21:14:518849388 4.28.X.X > 94.102.XX.XX 142
20:21:15:370662851 94.102.XX.XX > 217.153.X.X 65
20:21:15:437401662 94.102.XX.XX > 82.166.X.X 65
20:21:16:371366478 94.102.XX.XX > 61.93.X.X 65
20:21:16:686433904 61.93.X.X > 94.102.XX.XX 142
20:21:17:372028662 82.166.X.X > 94.102.XX.XX 141
20:21:17:469587225 82.166.X.X > 94.102.XX.XX 141
LOG

my %pending;

open my $fIn, '<', \$logStr;

while (defined (my $line = <$fIn>)) {
    chomp $line;
    my ($time, $ipFrom, undef, $ipTo, $len) = split /\s+/, $line;
    
    if (! exists $pending{$ipFrom}) {
        $pending{$ipTo} = {time => $time, from => $ipFrom};
        next;
    }
    
    my $delta = deltaSecs($time, $pending{$ipFrom}{time});
    print <<REPORT;
From $ipTo at $pending{$ipFrom}{time} to $ipFrom received at $time. Delta $delta
REPORT
    delete $pending{$ipFrom};
}


sub deltaSecs {
    my ($time1, $time2) = @_;
    my @t1Parts = split /:/, $time1;
    my @t2Parts = split /:/, $time2;
    
    $t1Parts[$_] -= $t2Parts[$_] for 0 .. $#t1Parts;
    
    return 3600 * $t1Parts[0] + 60 * $t1Parts[1] + $t1Parts[2] + $t1Parts[3] * 1e-9;
}

##</code><code>##

From 94.102.XX.XX at 20:21:09:366500902 to 63.77.X.X received at 20:21:09:484721194. Delta 0.118220292
From 94.102.XX.XX at 20:21:10:367148691 to 81.192.X.X received at 20:21:10:432251992. Delta 0.065103301
From 94.102.XX.XX at 20:21:11:367836444 to 103.229.X.X received at 20:21:11:665980944. Delta 0.2981445
From 94.102.XX.XX at 20:21:12:368606359 to 69.33.X.X received at 20:21:12:588588107. Delta 0.219981748
From 94.102.XX.XX at 20:21:13:369344850 to 85.32.X.X received at 20:21:13:396157789. Delta 0.026812939
From 94.102.XX.XX at 20:21:14:369986605 to 4.28.X.X received at 20:21:14:518849388. Delta 0.148862783
From 94.102.XX.XX at 20:21:16:371366478 to 61.93.X.X received at 20:21:16:686433904. Delta 0.315067426
From 94.102.XX.XX at 20:21:15:437401662 to 82.166.X.X received at 20:21:17:372028662. Delta 1.934627