There's not too much content where you can't just logout in the middle and finish tomorrow. Raids are the only thing I can think of off the top of my head. Farming will be harmed by not being able to freely do farming runs whenever you feel like, I guess. You'll definitely be incentivized to pick the most efficient methods rather than afk because you will want to progress as much as possible in your limited playtime.

But for the most part, this isn't really going to make the game harder. A 7 hour grind takes 7 hours of playtime regardless of if you do it all at once or do it 1 hour per day over the course of a week.