From personal experience, dinner in Ireland is between 6 and 9 PM but in some cases later.
I usually eat early and did get dinners at 6 PM, many diners did come in around 7, the time I left, but in some more expensive places people would just come in around that time and make reservations for later in the evening.
I would say, like in many countries, it depends on the class of restaurant as well as on the location.
So if you want to go for a late dinner, walk or call in earlier in the evening and try to make a reservation.
For lunch I tend to do sandwiches but on the few occasions that I had a day tour, the lunch stop was between noon and 2 PM, likely pubs and restaurants have lunch then, maybe lasting a bit longer.
Of course, there are all day food places, which close when the local shops do, but those are not restaurants nor pubs.