So then the real benefit of closed-mindedness is this: it saves you the time of having to entertain silly notions.

In this context it basically means that you spend less time in fun discussion with the female neuroscience PHD student? What's so awful about chatting with girls? I think it's a more fun topic of conversation than the weather. Don't attach yourself to judging the idea but play and explore the idea.

A key ingredient of being open minded is to avoiding being judgemental. You don't have to judge ideas. You can just play.