I personally 'rank' my full day interviews. I put them off until I have a good sample of companies lined up. Then I line up my 'best' company first, and the 'worst' company last. Basically, the goal is that by the time I get to the company i'm not as interested in, I have an offer from another one. That way I can frankly tender my resignation in before I get to that interview. I may or may not complete the last interviews depending.

In my case I didn't do a satisfactory initial call with the recruiters to ask them what the interview was going to be about, the level of the folks asking the questions and the possibility of doing it over a few days. They pulled the "we're excited to move forward..." trick, without saying too much about having to talk for 6 hours to very junior devs.