function calc_title() {
var time_of_day;
var date = new Date();
var hours = date.getHours(); 

if (hours >= 6) { time_of_day = 'morning';}
if ((hours >= 12) && (hours < 18)) { time_of_day = 'day';}
if (hours >= 18) { time_of_day = 'evening';}
if ((hours >= 0) && (hours < 6)){ time_of_day = 'night';}

return time_of_day;
}