Realize further that your mood may be determined by only a few people. A smiling nodder will make you feel good, and you will do better. People reading newspapers will make you feel bad, and you will do worse. Do not permit people to do things that make you feel bad. Schedule the talk for 11 a.m.
Most people are awake by then and few have gone back to sleep.
Late afternoon is also bad since some people will be running out of gas and others will be itchy to get off to some squash game or something. Never speak after dinner unless your talk is strictly joke and astonishment oriented. It is hard to get a lecture started and stopped smoothly. In starting, the problem is to attract attention and get people quiet. If you just start talking, your first words will be lost, annoyingly.