you can do this with a shortcode like this

    add_shortcode("custom_text_se282078", function ($attr, $content, $tag) {
    	
    	$result = "";
    	
    	if (date_i18n("H") > 15) {
    		$result = "It's after 15 h.";
    	} else {
    		$result = "It's before 15 h.";
    	}
    	
    	return $result;
    	
    });

with that you just have to put `[custom_text_se282078]` in the page