Do not take time zones into account, it doesn't work.
Eat at the time you eat when you are at home, so if when your none on vacation, you eat at 6 pm, book 6 pm on the ship, if at home you eat st 8.15 pm every night book that.
It's a misnomer this old wives tale.
On ship you and children adjust quickly to the sunlight, so the family is excited you will be up early on ship or in port say 8 am hsve breakfast, lunch on ship from noon to 1.30 or in port or castaway from 11.30 to 1.30.
So you are on local time for them, but then switch back to home time for dinner, IE a gap of 7 hours from lunch to 8.15 pm.
Eating late is bad for people's health, we over eat on a cruise, well we all do it, but then add unlimited soda, that needs to go " down" bodies process food better in the morning, worse in the afternoon, and badly at night. The old saying is, have breakfast like a king, lunch like a prince and dinner like a pauper.
Acid reflux, upset tummy, diabetes, are all made far worse the later you eat at night, so main dinner then a show allows your body to process food, but later dinner eating up to 10.15 lays on your tummy.
Now yes in Spain they eat late that's thier culture, if you like eating at 8.15 at home, do it, but do not adjust for time zones that never ever works.
With your children's ages, IMHO eating other than on main, will mess them up, they are used to eating at 6pm, they will hit the pizza and buglers at 6 pm, messing up a good meal, and then at 8.15 will be far too tiered to eat, messing thier evening up, they would gave been up from 7 am/8 am eaten breakfast and lunch ship time, so Late dinner is too long for them. Late is for adults and old teens only, and ask yourself, why, MAIN dinner always sells out first, as those with children avoid late and meltdowns.
On a Panama cruise you get an " hour" change on certain nights, so it's gradual and not noticed, west bound that's a short lay in, or the kids are still up early anyway and even more burnt out the following night, bring up an extra hour.