According to california vehicle code section 22651, your vehicle can get impounded by the police if the registration expiration date is more than before the date it''s found or operated on the highway, public lands, or an off-street parking facility.

The answer is more than 6 months.
In order to cancel the impounding process, owner must give  “Notice of Parking Violation” (citation) that will be issued by authority section of the California Vehicle Code tow away befor it will be cancellrf. For every evidence that deemed as correct and relevant to the cancellation, the amount of money needed for bailout will be reduced by $ 10