There is no law in California that requires a business to have an office there ("here" for me). However, to transact business in California beyond just an isolated transaction or two, a company must be registered with the California Secretary of State as a foreign entity (entities established in different states are considered foreign, as well as from other countries). I'll check on whether they have registered yet, but doubt they have.
As far as office real estate, it can be difficult to come by in silicon valley, depending on if it's 1999 or 2001 conditions! It's probably somewhat tight right now, but if they are getting, say, 3,000 to 5,000 feet, they'd likely hire a broker and get proposals from at least three landlords, then the lease itself is generally negotiated somewhat, especially if it from a longer period that a couple of years. It can easily take two to three months to find and lease space, then there usually is a tenant improvement period, which could be a week, if it's more or less paint and carpet, or a couple more months if more elaborate.
Even if they are doing a sublease for space, in which case it's less likely there would be much in the way of TI's, it can still be a process to negotiate the sublease and then get the master lessor's consent.
Or even their permanent space may only be 1,200 feet, with a shared receptionist type deal, which would be pretty easy and quick.
