dude that might take nearly a month. reconsider

OK as monocle_layton said, about 2900 miles from NY to Cali.

2900 miles divided by 3 mph would be 966 hours. divided by 24 hours equals 40 days.

It mostly depends on why they are visiting, typically six months is the soft limit, but considering the exceptional circumstances they might give him longer. 

http://traveltips.usatoday.com/long-can-stay-usa-tourist-visa-62787.html

"The visa or the completed Visa Waiver Program document permits non-immigrant travelers to enter upon U.S. soil only to the extent that they can present themselves to a determining Department of Homeland Security official. The official and his work station are euphemistically referred to as "the gate." The document that demonstrates permission to enter the country has been granted is universally called an I-94 -- the proper term is Arrival/Departure Record -- and it is issued by the determining officer at the gate. In simple terms, the visa allows the traveler to knock on the door; the I-94 card is proof the Department of Homeland Security has allowed them to come in. The I-94 determines the time limit of the stay, and the restrictions imposed upon the visitor while in the U.S. Visas do not allow any stay of any length within the U.S.

The unofficial posture is that few people can afford to live without working for more than six months. Because people coming to the U.S. on B2 visas are not allowed to work, they will in all likelihood be issued a maximum six-month I-94. If the entrant is seeking medical treatment that may quite reasonably be expected to take more than six months, the determining officer can issue a one-year I-94 without consulting a supervisor. A traveler with a B1 professional visa, meaning they have work the State Department has already determined is acceptable under all its conditions, can stay up to three years on a single I-94. In an extreme circumstance, then, a person with a one-month B1 visa could legally stay in the USA for three years, not one month."

Head west, and yes never walk alone, it's the usa after all.
There is a little mountain range in the way too.

https://www.google.ca/maps/dir/New+York,+USA/Los+Angeles,+California,+USA/@37.1029435,-105.1151406,5z/data=!3m1!4b1!4m16!4m15!1m5!1m1!1s0x89c24fa5d33f083b:0xc80b8f06e177fe62!2m2!1d-74.0059728!2d40.7127753!1m5!1m1!1s0x80c2c75ddc27da13:0xe22fdf6f254608f4!2m2!1d-118.2436849!2d34.0522342!2m1!1b1!3e2

913h 4,450km 27km height difference Goodluck!

That's some undertaking, and not just because of the distance.  You'll be spending the vast majority of your time walking through "flyover country", and the terrain will eat you alive once you get towards the Rocky Mountains and later the desert.

If you want to try something in the States that's much more manageable but still poses a big challenge, you can try walking from New York (presumably NYC as a starting point) to Miami (south Florida). The route is much more direct, and the terrain / climate a helluvalot more friendly.

Its highly ambitious, that's for sure, i get pissed just having to walk from my room to the bathroom

Sure. Mr F. Gump did it, twice. Even with company the second time.

'One does not simply walk into California'

Not bold enough, walk through every state and visit every capital.

If you can survive that, kudos.

Your biggest problem is going to be getting a support vehicle and someone who can take three months off of work to do it with you, with said person being a trained medic or at least someone who has experience with extreme foot injuries and blistering, there are portions of that treck in which you would be walking from the moment you get up till the moment you sleep, several days just to cross a section of land where every single mile will feel like then mile before it.

Personally I think it's too much to try off the bat, you're not Forrest Gump, maybe repeat the previous walk a few times in preparation, such as repeat it but once you arrive at the destination turn 180 and walk back, because when you make it all the way back you'll have done roughly 1/8th of the distance needed for crossing America.

So support vehicle and medic for 3+ months food and water for at minimum, 2 people for 3 months, medical supplies, fuel, good tracking and mapping, all as just a bare minimum.