For #1, I know many YC founders who have gotten in just using half or day or so for the application (usually defying the deadline). We used only one Sunday afternoon for ours on the second run when we got in and I don't see the point of wasting time except getting few rounds of feedback and spellcheck.

Interestingly enough also many alumnus I know thought they failed the interview once walking out of the room. I sure did.

Edit: With the second comment I was referring to section "Once we got the Interview, we knew we were in"