In the Reddit thread, u/Pearls_and_Flats gives several reasons why Friday is a terrible choice for having their family dinners, essentially boiling it down to the fact that all three of the women would have other things to do on Friday nights. Emily, as a socialite, would likely have fancy events to attend, Lorelai would probably need to be at the inn she owns, to host events and take care of potential emergencies, and Rory is a teenager who would probably much rather be out on dates or at parties. As u/pinkpink0430 said, “Sunday night dinners would solve so many problems.”
But it’s likely because of those other options that Emily insists on Friday nights. “It’s ~because it’s the most inconvenient and wack night,” u/doyoulovethebeatle said. “Emily loves power.” u/Poutine_My_Mouth agreed, adding, “Yeah, and if they have to cancel because of a social event, a make up night is another thing they owe to Emily.” It seems to illustrate how controlling Emily and Richard are over Lorelai’s life.
However, one Redditor poked a hole in u/Pearls_and_Flats’ theory. “Fundraisers and fancy corporate dinners actually rarely happen on Fridays,” they said, explaining that they’re usually on Saturday evenings, to give women the day to prepare. But they also acknowledged Emily’s exertion of power. “Friday night makes the most sense for Richard & Emily, and they were both significantly more selfish at the beginning of the series so what do they care if it inconveniences Lorelai and Rory?” they continued.