AM or PM?

I love to have something blooming the entire growing season. I also like to have something blooming the entire day. The morning glories grace the early mornings, the "regular" flowers open later in the morning and close again as the day wanes and the four o'clocks liven up the garden late in the day.

That was the plan. But, of course, this is MY garden and strange stuff happens. Here's another one to add to the Weirdness Chronicles.

This is what my four o'clocks look like when I get home from work in the morning:



And this is what they look like when I get up late in the afternoon:





So my question is, are four o'clocks supposed to bloom at 4:00 AM or 4:00 PM?