Setup: Superlux HD668B straight from Toshiba Laptop, with Equalizer APO to reduce the harsh treble on the 668B, and most of the time I was with crossfeed on just because I'm used to it (took it off for some of the spectral tests). Took me about an hour and a half, though I have an advantage since I have used Harman how to listen before. Speaking of which, has it been linked to in this thread? it's a bit more challenging than golden ears IMO: http://harmanhowtolisten.blogspot.co.il/
Edit: Hardest test for me was probably mp3 artifacts, though I didn't make any mistakes, just took a while. My first mistake was in frequency bands in music (in which I made several mistakes), and I also made one mistake in low frequency extension.
Also, here are the Equalizer APO files I use for the HD668B for those interested:
EQ:
Preamp: -6 dB
Filter 1: ON Pk Fc 2300 Hz Gain -3 dB Q 0.9
Filter 2: ON Pk Fc 5500 Hz Gain -6 dB Q 5
Filter 3: ON Pk Fc 9000 Hz Gain -3 dB Q 1
Filter 4: ON HSC 23 dB Fc 5300 Hz Gain -6 dB
Filter 5: ON LS 12 dB Fc 45 Hz Gain 6 dB
Crossfeed:
Copy: L2=L R2=R
Channel: L2 R2
Preamp: -4 dB
Filter: ON HSC 3dB Fc 430 Hz Gain -3 dB
Filter: ON HSC 3dB Fc 3300 Hz Gain -5 dB
Delay: 0.2 ms
Channel: L R
Filter: ON LSC 1.3 dB Fc 470 Gain -3 dB
Copy: L=0.5*L+0.5*R2 R=0.5*R+0.5*L2