Clouds are cutting bad at some folks framerate (reading your specs I believe they would for you too), so their ammount was limited to make the game playable for people with low-end machines. Keep looking for them, they are there.
As for the sunset/rise, AH's internal clock runs in realtime I think. Nights are currently cut out tho, but that still makes for about 12 hour day-cycles. I guess you just haven't been at the right times.
Look at the clock somewhere in your cockpit, it will show the ingame time. Sun rises at about 6AM and it sets at about 6PM. Like I said it magically jumps over the night at the moment.
