I booked my upcoming Mexican Riviera cruise 3 months ago, in July. When I booked (online), only second seating was available. I logged in a week or two later and I noticed the option to switch to first seating, which I did. Does that mean there was nobody on the waitlist?? I find that hard to believe. I was never on any list and was able to switch seatings easily, less than 3 months before the cruise. Maybe I just got lucky.
Only once did we ever have an issue. It was on a Carnival cruise last year. Carnival has four dining times. We had requested the 6:15 seating (or, second early seating) -- no waitlist -- but learned when we boarded that we had the 8:30 seating. The maitre d' told everyone that any changes would take effect the second evening. So, we ate at 8:30 the first night (BTW, our son's bedtime at home is 8:30, so this was tough), and learned the next day that we were reassigned to the 6:15 dining time.
My point in this rambling is that if you don't like your dining time (or are assigned Anytime Dining when you'd prefer a set dining time--or vice versa), see the maitre d' soon after boarding (this is usually noted in the ship's daily program; if not, s/he is usually in one of the main dining rooms). They can't always guarantee you your choice, but you'd have no chance if you don't ask.
A few weeks ago while on the Empress of the Seas (RCCL) we booked a transatlantic cruise for the end of March on the Jewel of the Seas. We want first seating but it is full so we are assigned to second seating and are wait listed for the first seating. I'm guessing there will be a lot of platinum and diamond members who will have priority over us newbies. (We'll be platinum members after that cruise.) I'm not sure if we will get early seating. If we don't and there isn't a choice of one portion of the dining room being open seating we may opt out of eating in the dining room altogether. We'll be sure to notify the Matre-D of our choice so a waiter isn't waiting for us. We can tip the waiters in the Windjammer or Room Service. And we'll still dress up on formal nights. I just don't like to eat that late, especially when we'll be losing an hour a day anyway. I hope we get early seating but will adjust if we don't.