Question

I couldn’t find the actual function’s code as I am interested in how it creates the id, e.g. where it gets the time from.

Answer 1

If you’re still interested in the source, it’s in the public git repository:
https://github.com/php/php-src/blob/master/ext/standard/uniqid.c

gettimeofday((struct timeval *) &tv, (struct timezone *) NULL);
sec = (int) tv.tv_sec;
usec = (int) (tv.tv_usec % 0x100000);

/* The max value usec can have is 0xF423F, so we use only five hex
* digits for usecs.
*/
if (more_entropy) {
    spprintf(&uniqid, 0, "%s%08x%05x%.8F", prefix, sec, usec, php_combined_lcg(TSRMLS_C) * 10);
} else {
    spprintf(&uniqid, 0, "%s%08x%05x", prefix, sec, usec);
}

RETURN_STRING(uniqid, 0);