I don't see the sense in doing any more than greeting on form open, and only if that form is a startup form. A greeting is a one time thing, no? If 2 people meet in the same locale they greet each other once "Good morning". After a few hours they go for lunch and meet up again at the same place after. Do they say "Good afternoon"? I think not likely. Besides, a timer with any span will always be late at some point. If I start the app at 10:00 AM, 6 hours later the greeting is 2 hours late, notwithstanding that it's only required once, so that form should not be a normally used form unless you set some sort of flag to prevent repetition.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.