use strict;
use warnings;

open my $logFH, q{<}, \ <<EOD or die qq{open: <<HEREDOC: $!\n};
Script /opt/OV/bin/OpC/agtinstall/inst.sh invoked by root at 02/25/11
14:36:48
Other stuff here
Script /opt/OV/bin/OpC/agtinstall/inst.sh invoked by root at 02/25/11 14:36:48
more stuff
and more
Script /opt/OV/bin/OpC/agtinstall/inst.sh invoked by root at 02/25/11
14:36:48
more guff
EOD

my $rxDate = qr{(?x) ( (?:\d\d/){2}\d\d ) };
my $rxTime = qr{(?x) ( (?:\d\d:){2}\d\d ) };

while ( defined( my $line = <$logFH> ) )
{
    next unless $line =~
       m{(?x)
            ^
            Script \s
            \S+ \s
            invoked \s by \s root \s at \s
            $rxDate
            (?: \s $rxTime )?
        };
    my $date = $1;
    my $time =
       defined $2
       ? $2
       : do {
          defined( $line = <$logFH> )
             or die qq{Unexpected EOF\n};
          $line =~ $rxTime ? $1 : q{No time found};
          }; 
    my $timestamp = join q{ }, $date, $time;
    print qq{Timestamp: $timestamp\n};
}

close $logFH
   or die qq{close: <<HEREDOC: $!\n};