It's a single snapshot taken once per day. I believe the Aqua satellite crosses the equator from south to north in the evening, so the Mozambique Channel, to use your example, would probably be measured around early afternoon. So the missing values would not be accurate averages of daily cloud cover. But the time would be fairly consistent every day, if that's useful.

Thank you very much for these informations Maria, you really helped. Have a nice day !