Question

If I run the following in PHP:

echo mktime(0,0,0,1,1,1970);

the returned value is -3600, not 0 as I expected.

The server is UK based, it’s currently 21 Sep (i.e. BST summertime) (though I wouldn’t expect this to affect the epoch timestamp) and per php.info: “Default timezone Europe/London”.

Setting the daylight saving time flag also, as follows, gives:

echo mktime(0,0,0,1,1,1970,0); (i.e. the correct DST flag, 0 as 1 Jan not DST/BST)
returns -3600

echo mktime(0,0,0,1,1,1970,1); (the incorrect flag – setting 1 Jan as DST)
returns -7200

echo mktime(0,0,0,1,1,1970,-1); (i.e. DST flag not set – left to PHP to decide)
returns -3600

Does anyone know why the epoch would be returned as -3600, not 0, please?

Answer 1

When it was midnight on Jan 1st 1970 in British Summer Time, it was one hour to midnight in Greenwich Mean Time. Try setting the time zone to UTC instead:

date_default_timezone_set('UTC'); // or just change php.ini