function display_title() {
datt = new Date();
var hours = datt.getHours();
if (hours >= 6) { time_of_day = 'Доброе утро';}
if ((hours >= 12) && (hours < 18)) { time_of_day = 'Добрый день';}
if (hours >= 18) { time_of_day = 'Добрый вечер';}
if ((hours >= 0) && (hours < 6)){ time_of_day = 'Доброй ночи';}
return time_of_day;
}

$(document).ready(function(){
  $("span#daytime").html(display_title());
})