<?
                $today = new DateTime();
                $begin = new DateTime('January 01');
                $ny1 = new DateTime('December 20');
                $ny2 = new DateTime('January 8');
                $spring = new DateTime('March 01');
                $summer = new DateTime('June 01');
                $fall = new DateTime('September 01');
                $winter = new DateTime('December 01');
                switch (true) {
                    case $today >= $ny1 || $today < $ny2:
                        echo 'Новогоднее настроение';
                        break;

                    case ($today >= $winter || $today >= $begin) && $today < $spring:
                        echo 'Зимнее настроение';
                        break;

                    case $today >= $spring && $today < $summer:
                        echo 'Весеннее настроение';
                        break;

                    case $today >= $summer && $today < $fall:
                        echo 'Летнее настроение';
                        break;

                    case $today >= $fall && $today < $winter:
                        echo 'Осеннее настроение';
                        break;
                    default:
                        break;
                }
                ?>