A git hook that won't let you commit on Tuesday or Wednesday in preparation for BC Break Thursday.

pre-commit

#!/usr/bin/env php 
<?php
/**
 * @installation Copy this file to .git/hooks/pre-commit if 
 *               you do not have any pre-commit hooks. 
 * @policy Enforce BC Break Thursday
 * @desc If we are within 2 days of Thursday, do not
 *       accept commits.
 */

// Work-around for ini-less PHP 5.4+ installs which require a 
// timezone to be set.
date_default_timezone_set(ini_get('date.timezone') ?: 'UTC');

$today = new DateTime();

if ($today->format('l') === 'Thursday') {
    // accept
    exit(0);
}
$nextThursday = new DateTime("next Thursday");
$diffTillThursday = $nextThursday->diff($today);

if (((int)$diffTillThursday->format("%d")) <= 2) {
    //reject

    // use PHP_EOL for that (weird) Windows guy
    fprintf(STDERR, "Error: you must wait for BC Break Thursday%s", PHP_EOL);
    exit(1);
}

// accept
exit(0);