Grew up Catholic. Translated this as "Friday" instead of "Thursday" on the first try and then I had to go back and correct myself.
As of my understanding, в + accusative shows a one-time occurrence, while по + dative implies a reoccurring event.
«По четвергам, он ест рыбу» – ‘He eats fish on Thursdays.’
«В четверг, он ел/будет есть рыбу» – ‘He ate/will eat fish this Thursday.’
Is that right?
Yes, that’s right.
(Also note that, unlike in English, you don't need the comma after adverbial expressions at the beginning of a sentence.)
Is the stress on the wrong part of Thursday here? I thought it was по четвергАм