Are you sure CA has the same rules as the IRS?

Yes, I checked

 Did you try entering -1? That's frequently Lacerte's version of zero.

Tried that - it says 'valid values are 1 to 365'

What you see is a Critical Diagnostic Warning the key word is Warning. https://proconnect.intuit.com/community/individual/help/diagnostics-and-suggestions-faq/00/97687

https://www.ftb.ca.gov/forms/2019/2019-1540.html#ParentStepparentFatherorMother clearly shows that the parent need not live with you. You should be able to go ahead and e-file and FTB has the knowledge to put parent and zero days together. 

The main reason to file 3532 is to avoid a letter from FTB, but sometimes FTB will still send out a follow up letter. With any HOH, tell the client to be sure to maintain records. "You must be entitled to claim a Dependent Exemption Credit for your parent. That is, your parent must meet the requirements of a qualifying relative and you must have paid more than half the cost of keeping up a home that was your parent’s main home for the entire year. Your parent’s main home could have been his or her own home, such as a house or apartment, or could have been any other living accommodation."

Thank you George,

So what you are saying is to basically override the critical warning, since we know the answer is correct with zero days.