PHP exec run in background still waits for command in for loop

Question

I've got a PHP for loop that runs 3 times and executes a command. The command it executes has a sleep(3) in there, but despite using nohup and attempting to run in background, my for loop is waiting 3 seconds on each iteration of my loop.

Why isn't my code executing this in it's own process and moving to the next to free up another loop?

<?php

class ScheduleRunTask extends AppShell {

    /**
    * Get command to run
    */
    protected function getCommand() {
        return 'cd ' . APP . " && Console/cake queue_manager process";
    }

    /**
    * Main execute task
    */
    public function execute() {
        $maxWorkers = 3;

        for ($workers = 0; $workers < $maxWorkers; $workers++) {
            $this->out('running...');
            $cmd = $this->getCommand();


            exec('nohup ' . $cmd . ' >> /dev/null 2>&1 & echo $!', $pid);
            $this->out($pid);
        }
    }
}