Well, you'll need to turn the lights on sometime because your betta needs a normal day/night cycle.
Usually it's 12 on/12 off, but some people do 8 on/16 off. As long as you're not in a sunny window, more than likely you won't have to worry about algae. Some tanks seem to get it worse than others. If you *do* start to have algae problems, you can purchase some quick growing live plants, like wisteria, java moss, marimo moss (not a fast grower, but good for algae control), anachris, duck weed, and they'll take all the nutrients and will starve your algae. Just don't put in fertilizer with these guys if you're combating algae. Mine all grow really well with just fish waste, so they'll do fine without anything additional. :)
I wouldn't worry too much about algae unless you it starts to grow. It's just borrowing trouble. :) Just make sure your tank is not in a window or somewhere that gets daily direct sunlight, that *will* cause it to grow. :)