Severus received the note in the middle of a class and made them wait until he was finished with his duties as a teacher, potion master and head of house. He knew that it would annoy Albus that he let him wait for so long, but Severus wasn’t regretting it, because he had duties and if Albus asked, Severus would just point out that he had things to do as a teacher, potion master and head of house.