An easy solution is to buy a timer, which you can find at hardware stores for between $6 and $20. You'll eventually save money on electricity. I'm not sure if it would harm them, but chances are it either: 1. Would harm them. or 2. Wouldn't help them. Either way, I'd rather save the electricity and not risk it.
14 hours of light seems to be typical. Even in nature they get more than 9 hours. The earth is round, we have 24 hour days, so on average they get about 12 hours of sunlight (yeah I know it varies, I'm simplifying).