Very odd, my opinion this code should work:
$(".entity-timeline").eq(0).on("loaded", HideArrowElements);
but somehow I can't get it to work here on my environment
as a non-pretty solution you can have the following:
setTimeout(HideArrowElements, 3000);
this will wait 3 seconds until trigger the function, does the job, but ideally you should be looking for the "loaded" event on the timeline element