I just did a 100 F smoke, I tried the fan on from start to finish, and the chips burnt up very quickly, so I added more, and did not use the fan while smoking. I turned the temp up a little, till I got smoke then back down to 100F, did that off and on for about 2 hours, then put the fan on.
Like NDKoze said, it took along time for everything to be done, mich longer than 12 hours for the last piece.