Ah I see, one of the times is on a new line. That wasn't immediately clear. Sorry. You could maybe use this although I've not tested it on a large file.

#!/usr/bin/perl

use strict;

my $data = do { local $/ = undef; <DATA>; };

while ($data =~ m/Script.+\sat\s(.+)\s(\n)?(\d+:\d+:\d+)/g){
 my $date = $1;
 my $time = $3;
 print "$date\t$time\n";
 }

__DATA__
Script /opt/OV/bin/OpC/agtinstall/inst.sh invoked by root at 02/25/11 
+14:36:48
blah
blah
blah
Script /opt/OV/bin/OpC/agtinstall/inst.sh invoked by root at 02/25/11
14:36:48
blah
blah
blah
[download]

Cheers