Legal Question in Landlord & Tenant Law in California

Actually, California statutes don't use the term "month" when referring to giving notice to end a lease. The statutes refer to "30 days" (for a residential lease of under one year) or "60 days" (for a residential lease of more tan a year).

If an actual lease agreement uses the term "month", then the word is given its plain meaning, except for February, which you have to add two days to (or one in leap years). If you want someone to leave in a month - let's say May 1 - then you need to give Notice on April 1.