enable at compile time?

[cupboy]

I found this article, but don't know what the guy meant by enabling at compile time. Can someone explain that further. And what is meant by "compile time"?

article:

date_create and other DateTime related functions are included by default only in PHP versions equal and greater than 5.2.

In PHP 5.1.2 this functionality is marked to be experimental and has to be enabled at compile time.

[scrupul0us]

it means, when php is compiled (./configure, make, make install) that option must be flagged in the configure argument