By David Mytton, CEO & Founder of Server Density. Published on the 22nd September, 2016.
Back in 2009 we introduced a new location preference feature for Server Density. Users could now specify their desired location, and then all dates/times automatically converted to their timezone (including handling of DST). We did that by using the DateTime class that was introduced with PHP 5.2.
Your very first challenge related to timezones is to deal with how they are calculated relative to the server’s default timezone setting. Since PHP 5.1, all the date/time functions create times in the server timezone of the server. And as of PHP 5.2 you can set the timezone programmatically using the date_default_timezone_set() function.
So, if you call the date() function—without specifying a timestamp as the second parameter and the timezone is set to GMT—then the date will default to the +0000 timezone. Equally, if you set the timezone to New York in winter time the timezone will be -0500 (-0400 in summer).