I think my main concern would be whether or not they'd allow it. Some schools really seem to think that anything out of the ordinary is "disruptive" and have an issue with it. "Outrageous" hair color, earrings and even long hair on guys, clothing that is outside of what they deem normal (for various reasons for both guys and gals)... they might have an issue with it, unless you think they might allow a guy to wear a kilt or if they've allowed someone in the past to do so.

Otherwise, I'm not sure when would be a good time to try it. If what I stated above could be an issue, what about waiting and talking to someone in the office about your desire to occasionally wear a kilt and explain the garment and everything behind it (to make sure they understand what it is) and see what they think?