When did BIP66 switch from activation to enforcement?
From BIP66:


  The new rules are in effect for every block (at height H) with nVersion = 3 and at least 750 out of 1000 blocks preceding it (with heights H-1000..H-1) also have nVersion = 3. Furthermore, when 950 out of the 1000 blocks preceding a block do have nVersion = 3, nVersion = 2 blocks become invalid, and all further blocks enforce the new rules.


I wrote this script to monitor the number of the last 1000 blocks that have nVersion set to 3.



require_once 'jsonRPCClient.php';

$daemon = new jsonRPCClient('http://{my_user}:{my_password}@127.0.0.1:8332/');
$blkStart = 364136 - (24 * 14 * 6);

$ver3InLast1000 = 0;
for ($i = $blkStart;; $i++) {
    try {
        $blockHashOld = $daemon-&gt;getblockhash($i-1000);
        $blockHashNew = $daemon-&gt;getblockhash($i);
        $blockOld = $daemon-&gt;getblock($blockHashOld);
        $blockNew = $daemon-&gt;getblock($blockHashNew);
    } catch(Exception $e) {
        break;
    }

    // Don't want to start subtracting until have processed 1000 blocks
    if ($blockOld["version"] == 3 &amp;&amp; ($i - $blkStart &gt;= 1000)) {
        $ver3InLast1000--;
    }

    if ($blockNew["version"] == 3) {
        $ver3InLast1000++;
    }

    if ($i - $blkStart &gt;= 1000) {
        echo "$i, $ver3InLast1000\n";
    }

}


The result can be found in this pastebin. 


  Block number 363724 is the block that turned on nVersion=3 enforcement for all further blocks.