Hens will generally lay almost every day. Out of 10 days, you'll typically get 9 eggs, most of the year. They'll slow down egg production in the winter due to the short days if you don't provide additional light (we keep a light going in the henhouse for heat during the cold part of winter, so we get a decent supply of eggs as a result, but you can expect maybe one egg every 3 days in november-january if you don't). They will typically go through a "molt" once a year where they'll lose a bunch of feathers and look really ugly and pitiful, and won't lay eggs during this period. Our hens don't go through this so much because of the additional light they get in the winter. Expect hens to lay pretty much until they die. They will slow down production as they get older, but you won't have a chicken "menopause" where they'll stop laying permanently. Hens can live 5 to 7 years, sometimes longer. I suppose when they die, you could cook them up to feed your dog, but we just bury them. In the city, you *might* be allowed to wrap them well and put them in the trash.
Additional information for you: chickens are very social creatures, so DON'T keep only one, keep at least two or three. You will ALWAYS find someone who will love to take extra eggs off your hands. Also, you need to feed them egg-layer's feed, which runs around 9 bucks per 50 pounds, and provide fresh water and a source of calcium (typically oyster shell, that you get at the feed store.) It is best to give them a place to run around to eat grass and bugs; don't keep them in a little cage or tiny pen, that's mean. Shut them up at night so predators don't eat them or they'll be gone in a week or two (owls, raccoons, coyotes, bobcats, etc all like to eat chicken.)
