In that case, go ahead and convert to UTC and save UTC as the relevant zone. In no case is timestamp+zone less flexible than UTC timestamp by itself.
The article is about saving datetimes. Usually calendars use datetime too.
If you need to count down X hours you are not looking to save a datetime. Maybe use an egg timer or the countdown feature of a smartphone.
That's not at all foolproof, although it works for the case the author describes and probably works for most people most of the time. It wouldn't work if, for some reason, I'm entering a calendar event for something I know will happen exactly n hours from now.