It's tricky, took me a bit to get a handle on it. Frisha is one of my favorite LI's in the game.
Anyways, when in doubt just keep listening in Dave and Frisha in his room on Wednesdays and Saturdays at 8pm. (You can start at during at 6, but you don't have to.)
Then listen in on Dave and Giron on Thursdays and Sundays. Giron doesn't wake up until 9:00 am. At noon he leaves to go the church. If you go listen to his conversation with the Pater in the church, Giron will stop leaving his office in noon. (Not necessary but it's handy thing to get his schedule more open, just walk up to him and the pater, and you will get the polygamy conversation). So to listen, 9 am to noon, if you haven't heard the convo in the church. 9 am to 6 pm if you have heard the polygamy bit. (The polygamy bit is important for future lore in that it will allow the MC to marry multiple women.)
Frisha's quest in game wouldn't update for quite a bit of the process, I think it's three cycles of listening at Dave's room and Giron's room before you can free her. All that time Frisha's quest will say the same thing. It won't update until after you choose to interrupt her and Dave, or not.
If Dave has cumwine in his room, then the game can interpret it as you wanting to do the NTR route where you watch Dave fuck Frisha. So if that isn't what you want, make sure you have swapped the wine in Dave's room.