I have booked cabin 3062 on this cruise in November. I was told to try to get deck 3, but near the front of the boat. I get seasick though, so I didn't take the very front.
I was told that that front cabin on deck 4 was available and it was convertible to double. I didn't want the very front of the boat though. I'd booked deck 2/3 outside, and when I called the cabin booking number they were giving me option to upgrade then.
Could it be worthwhile just booking outside 2/3 and then seeing what they have if you call to prebook a cabin? For £35 per cabin you could avoid noise, I'd say it's not worth paying £70 per person (and you may even end up paying another £35 and pre selecting a cabin number). Just my thoughts.
As for sail away. I'm guessing 12 midnight because that's when it was when we did this cruise on the topaz. The itinerary is switched around though, so it could well be different. Actually I have just looked at how close Las Palmas is (we previously went to La Palma first) and it is extremely close - so I'm going to say it must be midnight even though it's an 8am arrival at las Palmas.
As for mealtimes. We chose late sitting. We may end up eating in the Lido buffet anyway as we're vegetarians and the other one might not suit us. Early sitting is 630-7 according to their website and late is 8-9. I seem to remember reading it was 830 for late. I chose late because I thought if we're out all day (maybe late lunch ashore) and then get back aboard late (departure times from ports are sometimes quite late!) then you may want to relax and get ready and have a pre dinner drink or cocktail (I like the sound of the bar right up top). By then it could easily be 830.