The two most important contributions to when we sleep and how much we sleep are:
The things that influence are circadian rhythm are many, but by far the most important is light. That's what allows us to make adjustments when we travel from one side of the country to another; it's why we're jet-lagged for some period of time; it's what allows us to overcome jet-lag over a period of days. In particular morning light is going to be essential in setting our circadian rhythms.
For those individuals who have a sleep phase that is delayed - meaning that they prefer to go to sleep late and then wake up late - getting light at an earlier time will reset their clock; that is the equivalent of resetting their clock from Los Angeles time to Boston time when you get that earlier light. It's getting light earlier in Boston than it is in Los Angeles. So certainly for people who have difficulty falling asleep until, let's say, 2:00 am in the morning, and then can't wake up before 10 am, getting light before that 10am awakening, by forcing yourself to get up with an alarm, then exposing yourself to light at close range, for at least 30 minutes, can be invaluable for resetting your clock. Whether early light will be helpful for people who don't have a delay in their sleep phase is unclear, but it may be something worth experimenting with.
You don't need a light box to get light. In many parts of the country, it's getting light the old-fashioned way that's going to be helpful; that's just sitting in front of a window or going outside, which is much cheaper than buying a light box. The essential part is making sure that you get up - with an alarm, if necessary - and keeping your eyes open so that you're exposed to morning light, as a way of then setting your internal circadian rhythm so that you'll be able to fall asleep roughly 16 hours after that initial exposure to light.