The deadline to file a California mechanics lien will generally be 90 days, about 3 months, from the completion of the project. Note, though, that if a Notice of Completion or Cessation is filed, that time-frame will be shortened to 60 days from the date that notice was filed. For help calculating exact dates, Levelset has a helpful tool: Payment Rights Advisor.
For more background on the California mechanics lien deadlines and requirements, here's a great resource: California Mechanics Lien Guide and FAQs. And, for more info on how to actually proceed with a lien filing: How to File A California Mechanics Lien – Step By Step Guide To Get You Paid.