use strict;
use warnings;

# Skip headings line(s).

my $discard = <DATA> for 1 .. 1;

my $currentTimeStr = q{};
my @currentLines   = ();

while( <DATA> )
{
    my $timeStr = ( split m{,} )[ 3 ];
    $timeStr =~ s{\..*}{};
    if( $timeStr ne $currentTimeStr )
    {
        processLines( @currentLines )
           if @currentLines;
        $currentTimeStr = $timeStr;
        @currentLines   = ( $_ );
    }
    else
    {
        push @currentLines, $_;
    }
}
processLines( @currentLines );

sub processLines
{
    my @sortedLines =
       map  { $_->[ 0 ] }
       sort { $b->[ 1 ] <=> $a->[ 1 ] }
       map  { [ $_, ( split m{,|\n} )[ -1 ] ] }
       @_;
    print $sortedLines[ 0 ];
}

__END__
X,Y,Z,Time,Amplitude
2550,531,66,10-12-2007 07:03:08.069,2
2549,529,62,10-12-2007 07:03:08.151,1
2550,531,66,10-12-2007 07:03:09.069,1
2549,529,62,10-12-2007 07:03:09.151,2