The white specks could be chemicals in the water that leach out, and tend to crystalize on top of the soil, or on the rim of the flower pot. One way to avoid this in a larger pot is to water it so thoroughly when you water it, that quite a bit of water runs out of the bottom, thus flushing the "salts" out of the pot. Over time, the white stuff will grow in size, and parts will take on a brownish tinge, looking almost like rust. This leachate will not kill your plants, no longer than you have them in growing pots, but if you had a treasured house plant that had white deposits on the soil, it would be advised to repot it with fresh soil ever so often, maybe once a year.Even for little bitty pots, if they have adequate drainage, the best advice is to water them thoroughly when you water, and let the pots dry out slightly between waterings. You dont want to wait till the plants have wilted, but even then, unless they are really dried out, they will revive with watering.
If you can't afford the 4 or 5 dollars a timer would cost, my advice is to just leave the light on.