libraries/class-wp-session.php
protected function set_expiration() {
		$this->exp_variant = time() + (int) apply_filters( 'wp_session_expiration_variant', 24 * 60 );
		$this->expires     = time() + (int) apply_filters( 'wp_session_expiration', 30 * 60 );
	}
protected function set_expiration() {
		$this->exp_variant = time() + (int) apply_filters( 'wp_session_expiration_variant', 24 * 60 );
		$this->expires     = time() + (int) apply_filters( 'wp_session_expiration', 30 * 60 );
	}
Set both the expiration time and the expiration variant.

If the current time is below the variant, we don't update the session's expiration time. If it's
greater than the variant, then we update the expiration time in the database.  This prevents
writing to the database on every page load for active sessions and only updates the expiration
time if we're nearing when the session actually expires.

By default, the expiration time is set to 30 minutes.
By default, the expiration variant is set to 24 minutes.

As a result, the session expiration time - at a maximum - will only be written to the database once
every 24 minutes.  After 30 minutes, the session will have been expired. No cookie will be sent by
the browser, and the old session will be queued for deletion by the garbage collector.

@uses apply_filters Calls `wp_session_expiration_variant` to get the max update window for session data.
@uses apply_filters Calls `wp_session_expiration` to get the standard expiration time for sessions.