Stamps used to have a glue on the back that you had to breathe into life by adding moisture. You then had to stick the stamp to the paper envelope as the backing dried. Definitely before the backing dried, as then the stamp wouldn’t stick.
Waiting by the door for important news to arrive? The first post would tip through the letterbox early in the morning. Important news not there? Then you would wait patiently for the second post to occur, and that would happen somewhere between midday and 2pm.
For more than a century, telegrams brought urgent messages: bad news, congratulations at weddings, and announcements of new babies. Telegraph operators transmitted messages over wires by Morse code; these were printed out and hand-delivered by a messenger, often on a bicycle. Not exactly instant, then, but effective.