Well, depending on where you live, dinner could be a midday, late-afternoon/early-evening, or late-night meal. Lunch is usually a midday meal. In reality, there is no word for a meal in place of lunch and dinner (I assume you use dinner to mean an evening meal after a midday lunch.) Dinner could be the main meal of your day, and whether you have it at noon, two o'clock, five o'clock, or eight o'clock, it remains your dinner. If you are going to have a substantial meal after breakfast, with only a very late snack in view before bed, then that meal becomes your dinner, no matter how weird that sounds.
I should point out, though, that in this day and age, especially for the yuppies, formal mealtimes may not be the norm. Plus, the usage of dinner for a midday or mid-afternoon meal, and other such formalisms as tea, etc, may now be considered quite old-fashioned. Thus, I would recommend sticking with either late lunch or early dinner for this particular situation.