PHP 5.5.10 got released a few weeks ago, and among other things, it added some new functionality related to timezone handling.

In short, this is now works:

$tz = new DateTimeZone('UTC-05:00');

Normally this would not be recommended, as you really should specify timezones based on their geographical location. This information is not always available though, so it’s a welcome new feature.

The sabre/vobject project is a heavy user of timezone-related features, and unfortunately this introduced a few subtle bugs.

UTC vs. GMT

Before PHP 5.5.10, this code:

$tz = new DateTimeZone('GMT');
echo $tz->getName();

Would output:

UTC

Now, GMT no longer automatically gets converted to UTC, and the same script will now output GMT. UTC and GMT are very similar, and in most practical situation interchangeable. (but not all).

If you relied before on figuring out wether a time is in UTC, be careful, because you may have to change this to UTC or GMT.

Some timezone ids are now invalid

There’s quite a bit of weird timezones on the Other page on php.net. Even though these are not recommended to be used, we still need them as people may generate timezone ids from that list, which we need to understand and parse.

Since PHP 5.5.10, the following timezone identifiers from that list now throw errors:

CST6CDT
Cuba
Egypt
Eire
EST5EDT
Factory
GB-Eire
GMT0
Greenwich
Hongkong
Iceland
Iran
Israel
Jamaica
Japan
Kwajalein
Libya
MST7MDT
Navajo
NZ-CHAT
Poland
Portugal
PST8PDT
Singapore
Turkey
Universal
W-SU

This was reported as bug #66985.

Handling of some incorrect timezone names

The vobject library relies on exceptions to be thrown when constructing the DateTimeZone object. When this happens, a fallback behaviour kicks in that attempts to guess the correct timezone.

Microsoft often throws us timezones such as this:

(GMT+01.00) Sarajevo/Warsaw/Zagreb

This now automatically gets picked up as the ‘+01:00’ timezone by DateTimeZone, so as of PHP 5.5.10 the fallback behavior no longer kicks in, and we’re no longer returning `Europe/Sarajevo’.