So Yahoo! 知恵袋 (http://chiebukuro.yahoo.co.jp/) is great for answering obscure questions...

Today, I was wondering why 昼間 is pronounced ひる・ま (using 訓読み) while 夜間 is pronounced や・かん (using 音読み).

So I typed this into the search box:  "ひるま やかん" and it came up with this question:

昼間は、ひるまで夜間は、やかんでどうして音読み、訓読みで違うんですか？
(http://detail.chiebukuro.yahoo.co.jp/qa … 1416506559)

The explanation was detailed and pretty easy to understand.

Anyways, that site's also great for pulling example sentences from.