You said W.
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Simply put, this trek makes for the most amazing day. From the refuge, you should allow 3-4 hours to reach the summit. This should give you plenty of time to go easy on your legs and get the camera clicking away. When you are on the summit, you should be rewarded by the most amazing, far-reaching views. Don't underestimate the ascent and the effects of altitude. The descent back to the refuge (or Imlil if your legs will hold out) is 2.5 hours or 4-5 hours, respectively.