Yes, I usually do make it ahead. It is something I'll often have for lunch at work during the week, so for convenience and quickness, I tend to make it the night before. As long as you mix the pieces of avocado well in the mixture, then seal in an airtight container (like tupperware, for example) then I find that it's fine and doesn't turn.

Also, to clarify:
When I'm making it to take to work, I don't do this, preferring to cut up the whole avocado and mix it in, instead of leaving half to fan over the top.