This is actually a great question. The GMAT, especially the verbal section, is a test of endurance and focus as much as anything else.
I tried doing lots of RC and SC questions later at night, when focus is very tough and the mind is tired. I felt like this increased my tolerance and endurance, and prepared me for those last 30 minutes of the GMAT when the mental fatigue really starts to set in.
Also, when doing practice tests, it's fine to skip the AWAs on some of them, but it's also great practice to include the AWAs on some so that you get a real feel for how tired you will be when the real thing comes along.