The normal check in time is 3pm. To get access to rooms any earlier depends totally on how busy Hotel was the night before. I feel sure that if you call or email them they will do their very best to accommodate you. Hope you have a wonderful trip to Ireland especially if it is your first trip here. Safe travels.
I am not in a position to speak for the Greville Arms Hotel. I just had a really enjoyable stay there. I suggest you address all questions in relation to accommodation to the Management of the Greville Arms Hotel, which you can contact at 044-9348563.
ENJOY YOUR STAY!!!