I can't grasp what "normal" riding conditions are. Everyone does it a bit differently. I check my chain tension frequently, at least as often as I clean/lube it, which is 300 miles usually. But Manny hit it right on the money, adjustment is done on an "as needed" basis. Cleaning and lube is done on a periodic basis.
You pop on a new chain/sprkt setup and you have to do one or two quick adjustments as things settle in. Then adjustments (at least for me) are very infrequent for 10 K mi or so.
The fastest way that I have found to destroy a good chain is to run it too tight. I check my chain tension with the chain warm, with me sitting on the bike, and try to find the tightest section of the chain. If it is clearly too tight I will adjust it, carefully. If you carry passengers I would check it with a passenger aboard too.
Like Manny said, I adjust it as needed, but not that often. When frequent adjustments are required you will notice that the sprockets are getting worn, the bike surges and falls at steady low speeds, things just don't feel right.
Steve