Question

Is it possible to have something like?

$offset    = -05:00; 
$timezone  = getTimeZone($offset); //return America/New_York 
date_default_timezone_set($timezone);

How about the DST(Day Saving Light) if yes?

EDIT

What i have tried is

function php_date_default_timezone_set($GMT,$timestamp) { 
              $timezones = array( 
                  '-12:00'=>'Pacific/Kwajalein', 
                  '-11:00'=>'Pacific/Samoa', 
                  '-10:00'=>'Pacific/Honolulu', 
                  '-09:00'=>'America/Juneau', 
                  '-08:00'=>'America/Los_Angeles', 
                  '-07:00'=>'America/Denver', 
                  '-06:00'=>'America/Mexico_City', 
                  '-05:00'=>'America/New_York', 
                  '-04:00'=>'America/Caracas', 
                  '-03:30'=>'America/St_Johns', 
                  '-03:00'=>'America/Argentina/Buenos_Aires', 
                  '-02:00'=>'Atlantic/Azores',
                  '-01:00'=>'Atlantic/Azores', 
                  '+00:00'=>'Europe/London', 
                  '+01:00'=>'Europe/Paris', 
                  '+02:00'=>'Europe/Helsinki', 
                  '+03:00'=>'Europe/Moscow', 
                  '+03:30'=>'Asia/Tehran', 
                  '+04:00'=>'Asia/Baku', 
                  '+04:30'=>'Asia/Kabul', 
                  '+05:00'=>'Asia/Karachi', 
                  '+05:30'=>'Asia/Calcutta', 
                  '+06:00'=>'Asia/Colombo', 
                  '+07:00'=>'Asia/Bangkok', 
                  '+08:00'=>'Asia/Singapore', 
                  '+09:00'=>'Asia/Tokyo', 
                  '+09:00'=>'Australia/Darwin', 
                  '+10:00'=>'Pacific/Guam', 
                  '+11:00'=>'Asia/Magadan', 
                  '+12:00'=>'Asia/Kamchatka' 
              ); 

    date_default_timezone_set($timezones[$GMT]);

    return  date_default_timezone_get();
}  

    echo php_date_default_timezone_set('-05:00',time()); 
   // returns America/New_York

But i don’t know whether this way is correct or not?

Answer 1

No, because there’s no such reverse correlation. There are many timezones which currently have a -05:00 offset. That’s why you should use timezone identifiers to identify timezones, not offsets.