excerpt length on blog page

On that topic mentioned above – my solution to cut the excerpt by word count or something like this :

function custom_excerpt(){
?>
<script>
(function($){
	$(window).on('load' , function(){
	    $('.slide-entry').each(function() {
	     	$(".entry-content").text(function(index, currentText) {
	     		return currentText.substr(0, 20);
			});
			// if you like to cut the titles
	    	$(".entry-title").text(function(index, currentText) {
	     		return currentText.substr(0, 50);
			});
	    });
	});
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'custom_excerpt');

will work too – but better would be not to manipulate the DOM afterwards – but to directly build an excerpt with given settings.
so again : HOW to influence even these excerpts ?

no hurry – I just wanted to bring it up once because the topic came up now – and I honestly never checked that the manually pasted excerpts were not affected.
Many thanks as always

and how to use it – for setting excerpt_length ?

Yes