My wife and I will be traveling to Madrid in February. I've been to Madrid once before for a couple of days, but this will be my wife's first trip there. She is very particular about when she eats, and adaptability is not one of her strong suits. When we were in Italy last year, she kept asking why (and getting annoyed by) the fact that most restaurants didn't open until 7:30 or later for dinner. Spain will be a quantum leap for her, and not in a good way, with standard dinner being 9 PM or even later. Telling her the cold hard reality of "that's just the way the culture is, you'll need to adapt" has not exactly been productive to this point....

I was apprehensive about eating times too when I went to Madrid in 2008, but was able to adapt reasonably easily by eating many tapas at 6:30-7:00 and calling it dinner. We're likely to rent an Airbnb so we'll presumably have a kitchen and can eat some meals there, at whatever time we want, but we're not going to want to cook every night either. How can I help ease her transition into Spanish dinner habits?

How can I help ease her transition into Spanish dinner habits?

Rent an apartment where you can prepare a light snack when she needs it, then you can enjoy the later dinner hour at a restaurant without dying of hunger....
Or show her how much fun it is to buy fresh ingredients at the local market as you make her a full dinner yourself..

Plan and make time for your big meal at lunch, the way most Spaniards do. If you have a two hour restaurant meal that doesn't end until 2:30 or 3:00, eating a full meal at 6:00 doesn't appeal to most folks.

You don't have to actually "cook" to eat well when you rent an apartment. I don't (it would not be fun for me what J62 describes).

Just get to know the neighborhood nearby and find the delis, bakeries, shops, green grocers, street stalls, anyone with prepared items and "gather" foods to eat at home, whatever time of day you like. Make sure you have water, coffee, tea, wine, beer, beverages of choice, on hand.

I agree, have your hot restaurant meal out at lunch-time. Problem solved!

I wouldn't try to convince your wife to have dinner out in a restaurant at 10pm if she doesn't want to. I don't really see the point of that.

As per the experience of my travelers from the US and other countries with different eating times, the main thing is to focus on what´s "dinner" for us. Lunch is the most important meal of the day, what many visitors call "siesta" (can´t understand why, siesta (nap) is not that common, we have to work!), and it lasts around one hour, normally. Even much longer on weekends. But dinner is mainly unimportant, at least on weekdays, we have something very light (a soup, or an omelette, or a salad, a yoghourt and some cereals...but nothing too big), and your wife may have to know that your dinner is our lunch, and dinner is light. Tapas are not dinner for us (it´s something that goes with your drink, before lunch or dinner), but it may be a good solution.

As a matter of fact, we find it hard to believe that dinner in many countries is soooo very early, and wonder why...

either
get her to have a siesta during the afternoon and eat as the Spanish do
or
No siesta, nothing open, get bored and then tapas.

Rome, Roman candle!

It's not just the evening meal; all the meals in Spain are later than they are in the US.

Here's an idea: get two birds with one stone. Set your watches ahead just three hours instead of six (assuming you're from the east coast). That way your meals will be at the expected time and you'll have three hours less of jet lag.

<<Telling her the cold hard reality of "that's just the way the culture is, you'll need to adapt" has not exactly been productive to this point....How can I help ease her transition into Spanish dinner habits?>>

Sounds like you can't .
Go alone if that option is open.

She doesn't need to adapt. I'd be mad too if someone said that to me. If she's not interested in "transition into Spanish dinner habits" you are going to ruin the trip for both of you trying to force that issue. There are plenty of other ways to approach it including all the good suggestions already made above to make her feel comfortable, and eat at whatever time she wants to.

Oh for heaven's sake, just let her eat when she's hungry. This is hardly an earth-shattering travel issue. She'll manage, or she won't.

It depends on what kind of meals you are after.
If you are ok with any kind of food, there are no shortage of non-stop meals available.
There are also many restaurant, many good enough, that open at 7:30pm to allow early eating tourists before the locals come in much later in the evening.
If you are foodies looking for top dining experiences, these restaurants don't open until 8:30pm or 9:00pm.

Last trip to Spain was weird for me because there were so many festival days and nothing opened. I would eat lunch and something light at dinner. We were on and off base at Rota so ate several evening meals on base. I never found a grocery store opened. Cadiz was different, many places opened all day long. I would think Madrid would be the same. We stayed with friends there and they cooked.

We dealt with this very easily while in Spain. We just had a variety of Tapas around 6pm. It was a fun way to eat early and try an assortment of new foods.

Why should you have to cater to her and not vice versa? She wants to play diva, make your reservations for one - or just eat at the bar while she is home sulking.

[See, I told y'all when I hit 65 I would embrace my inner curmudgeon]

It'll be very interesting for my wife and I how we adapt when we go to Spain later this year. Luckily, we tend to be fairly adaptable.
For us, we often eat our big meal anytime between 5 and 7:30, and my wife (an early riser) tends to be in bed by 10:00.

Part of the fun of traveling is finding out about other's ways.

For some of you wondering about earlier eating hours:

Although this would not be typical of everyone, I find the usual times of eating for my friends and I in Seattle to be as follows:
Breakfast starting sometime between 7AM and 8AM, sometimes a bit later, Lunch being a light quick meal sometime around noon or 1:00, and Dinner, the big meal of the day, being at 5, 6, or 7, with 7:00 seeming to be the time that reservations are hardest to get in restaurants here.
In farming and rural areas on the western US, where we both grew up, the timing may be an hour earlier.
I imagine in some of the larger cities on the east coast timing may be an hour later.

But wow, 7:30 PM being an exceptionally early eating time? That will be a new experience for us. Looking forward to adapting.

>>> But wow, 7:30 PM being an exceptionally early eating time? That will be a new experience for us. Looking forward to adapting.
You will not see local families with small children coming out in mass until around 10 PM.
A part of this seemingly late behavior stems from the European time zone. Madrid and Rome are in the same time zone even though they are about 16 degree apart in longitude. This translates to about one hour difference in sunset time. For example, today July 24th, Rome sunset is 8:37 PM while it is 9:38 PM for Madrid. When you eat dinner at sunset, you will be naturally one hour later in Madrid compared to Rome.
On the other end of the spectrum are the Scandinavians. If you go to restaurants in Copenhagen at 6pm hoping to beat the crowd, it will be already busy.

As said...the main problem is considering lunch as in the US, something light and quick. Here it´s the very mean meal of the day (weekdays), while dinner is not important. Who´d have dinner at 7pm??? It just does not make any sense in our culture, you´re out on the streets socializing with friends, having a glass of wine, a pintxo or a tapa, and enjoying the company of others. Then you go home to have a light dinner...and of course, we go late to bed (TV shows end very late too). It´s cultural, but very easy to adapt to when you´re on vacation.