If you've been invited over for dinner, but can't stay for too long, is it ruder to eat and run or not go at all?

Say your first exam is the next morning, and you’ve finished your information sheet but were planning to do some past exam questions tonight. You were going to cook yourself some dinner and get into it.

Then, you are invited over for dinner at a neighbour’s house. They are good friends and know you have exams but you don’t see them very often despite the proximity of their residence and it would be nice to go.

Do you go, eat dinner, and politely excuse yourself to go home and study, possibly appearing as though you only went for the food?

Or do you politely decline and say thanks but no thanks maybe another time? (the “another time” isn’t likely to happen for a while.)