This is what the law says:
(a) The following persons may operate a motor vehicle in this state
without obtaining a driver’s license under this code:
(1) A nonresident over the age of 18 years having in his or her
immediate possession a valid driver’s license issued by a foreign
jurisdiction of which he or she is a resident, except as provided in
(a) (1) For purposes of this division only and notwithstanding Section
516, residency shall be determined as a person’s state of domicile.
“State of domicile” means the state where a person has his or her
true, fixed, and permanent home and principal residence and to which
he or she has manifested the intention of returning whenever he or she
Prima facie evidence of residency for driver’s licensing purposes
includes, but is not limited to, the following:
(A) Address where registered to vote.
(B) Payment of resident tuition at a public institution of higher
(C) Filing a homeowner’s property tax exemption.
(D) Other acts, occurrences, or events that indicate presence in the
state is more than temporary or transient.
(c) Any person entitled to an exemption under Section 12502, 12503, or
12504 may operate a motor vehicle in this state for not to exceed 10
days from the date he or she establishes residence in this state,
except that a person shall not operate a motor vehicle for employment
in this state after establishing residency without first obtaining a
license from the department.
So a nonresident can drive with an out-of-state driver's license. You can no longer drive with an out-of-state driver's license more than 10 days after "establishing residence" in California. Residence is defined as the "state of domicile", which is defined as "the state where a person has his or her true, fixed, and permanent home and principal residence and to which he or she has manifested the intention of returning whenever he or she is absent".
So you are considered to become a resident (and can drive with an out-of-state driver's license no longer than 10 days after) when California becomes your true, fixed, and permanent home and principal residence and to which you have manifested the intention of returning whenever you are absent. Whether that happens when your plane lands, when you start a job, or never happens during your stay, that is something you will have to determine based on your circumstances.