How does this feature work? It lists all the threads to which there has been a reply within the previous 24 hours?

for me I think it's since 12 a.m.?

I don't know, but I use it over the View new posts button

Yeah, I'm thinking it might be better.

only problem is that you have to go to the main page to get to it

view new posts is better imo because it allows you to see the ones that aren't even active. Sometimes if no one replies within a few minutes, it can move to page 2 but one reply and suddenly it can create a whole discussion which leads it to be active. (also I actually find some inactive ones interesting to read)