$twitter = new Twitter();
$twitter->setCredentials($config['username'], $config['password']);
$next_tweet = file_get_contents(dirname(__FILE__) . '/nextCoffeeTweet.txt');
$since_id = file_get_contents(dirname(__FILE__) . '/lastMention.txt');
$mentions = $twitter->getMentions($since_id);
if (!is_array($mentions)) {
    die;
}
foreach ($mentions as $mention) {
    if ((string) $mention->id > $since_id) {
        $since_id = (string) $mention->id;
    }
    if (strpos(strtolower($mention->text), 'wann') !== false || strpos(strtolower($mention->text), 'when') !== false) {
        $time = $next_tweet - time();
        if ($time <= 0) {
            $next_tweet = calculateNextCoffeeTweet();
            $time = $next_tweet - time();
        }
        if (date('w', $next_tweet) == 0 || date('w', $next_tweet) == 6) {
            $message = 'erst wieder am Montag';
        } else {
            if (date('d', $next_tweet) != date('d')) {
                if (date('w', $next_tweet) == 1 && date('w') == 5) {
                    $message = 'am Montag';
                } else {
                    if ($next_tweet - time() < 24 * 3600) {
                        $message = 'morgen';
                    } else {
                        $message = 'in ' . ceil(($next_tweet - time()) / 24 * 3600) . ' Tagen';
                    }
                }
<?php

require_once 'config.php';
require_once 'Twitter.php';
require_once 'functions.php';
$nct_file = 'nextCoffeeTweet.txt';
$nct = trim(file_get_contents(dirname(__FILE__) . '/' . $nct_file));
$now = time();
if ($nct == '') {
    file_put_contents(dirname(__FILE__) . '/' . $nct_file, calculateNextCoffeeTweet($now));
    die;
}
if ((int) $nct < $now) {
    $twitter = new Twitter();
    $twitter->setCredentials($config['username'], $config['password']);
    file_put_contents(dirname(__FILE__) . '/' . $nct_file, calculateNextCoffeeTweet($now));
    $tweet = sprintf('O HAI! Um %s Uhr ist es Zeit für die nächste Kaffeepause!', date('H:i', time() + 300));
    $twitter->update($tweet, 'xml', array('lat' => $config['lat'], 'long' => $config['long']));
}
<?php

require_once 'config.php';
require_once 'functions.php';
var_dump(date("r"));
$now = $beforelunch = mktime(12, 01);
var_dump(date("r", $now));
$nct = calculateNextCoffeeTweet($now);
var_dump(date("r", $nct));