I believe I've read that at about 5 months you can start weaning your dog from 3 to 4 times a day feedings to two or one times a day. The AMOUNT of food should be the same regardless of how many times a day you feed. If you feed a total of 4 1/2 cups of kibble a day (about right for a 6 month old pup), you can divide that up 2 or 3 times depending on how often you feed.
I've said before that I believe dogs have internal clocks too, just like humans, which tell them when to eat and sleep and so forth. I free feed Maggie now and she eats MORE than when I was feeding her 3 times a day and having to throw so much out because she wouldn't eat it when I put it down. Now she eats when she's hungry (she likes to eat later in the day and at night before bed) and she almost consistently eats at least 4 cups of kibble a day. She is growing marvelously and with all the exercise we get, her muscles are incredibly strong.
Use the chart on the dog food package as a rough guide as to how much to feed your dog according to its age and weight and prospective size (Boxers are considered Large Breed dogs). If you notice your dog eats better at certain of the four meals you put down, then you might want to try feeding more at those meals and slowly (over a couple of weeks) eliminate the meals she doesn't eat much of. (I hope I'm making sense here, its early and my coffee's not ready yet :D)
Good luck.
------------------
Dan from Brooklyn
Proud Pappa to Maggie Mae, Born 6/16/00
Flashy Fawn (Red), docked tail, natural ears.
Pictures:
http://maggie.artshost.com