Yes, they open in the morning, stay open all day as long as it isn't rainy or really overcast, then close up later in the day. I'm not sure if it is a lunar thing or relates to the light, but they may stay open longer for you if you have good later day day sun. My sun is gone from the pond by early afternoon and I think I remember them often closing between 4 and 5 ish. That may also vary by variety, but others would have a better idea of that.
If you were there until 9:00 and you had sun on the pond, I doubt you missed it, although it may have gotten to partially open later and then closed. By 9:00 you would probably see it starting to open. But I would be hopeful about tomorrow if it was already showing over the water yesterday.
I might suggest telling the office something like, "My first born isn't going to school today, so I'm going to be a little late this morning." Reality is what you make of it.
