正确的方法来定义CodeIgniter时区

I'm having some trouble making a platform using CodeIgniter to echo out the time in a specific timezone. According to the CI docs, if I wanted to output the timestamp in EST with DST on, I would use something similar to the following:

$timezone  = 'UM5';
$daylight_saving = TRUE;

My first thought was to just change the master time reference found in config.php to UM5 - but that didn't make anything change.

At this point I'm pretty sure I need to insert those above mentioned variables somewhere in the PHP page that I'm working with. The problem is, I'm not quite sure where I need to insert them.

This is what the current page looks like:

<?php 

class IG_Time extends CI_Model {

function __construct()
{
    // Call the Model constructor
    parent::__construct();
}

// return date and time in format selected by user
function GetDateTimeInFormat($datestamp, $format)
{
    switch($format)
    {
        // Swatch Internet Time
        case null:
        case 1:
            return date_format(date_create($datestamp), 'jS F, Y') . ' @' . date("B", human_to_unix($datestamp)) . ' .beats';
        // Unix time
        case 2:
            return human_to_unix($datestamp);
        // Time since
        case 3:
            return timespan(human_to_unix($datestamp), time()) . ' ago';
        // Database
        case 4:
            return $datestamp;
        // English
        case 5:
            return date_format(date_create($datestamp), 'jS F, Y, g:i a');
        // American
        case 6:
            return date_format(date_create($datestamp), 'F jS, Y, g:i a');

    }
}
}

I tried adding the $timezone and $daylight_saving variables directly under the opening

return date_format(date_create($datestamp,$timezone,$daylight_saving), 'F jS, Y, g:i a');

But that appeared to have broken the time completely, so I reverted back to it was by default.

Where would I need to place the $timezone and $daylight_saving variables and how should I use them trying to "return date_format".

Thanks in advance!

Put this code in index.php file on root

if( ! ini_get('date.timezone') )
{
   date_default_timezone_set('UM5');
}