The full vote-by-mail guide for your reference: Web Link.
When must I return the voted ballot?
In order to be counted, an elections official in your county of residence must receive your ballot no later than 8 p.m. on Election Day. Elections Code §§ 3020, 14212
You can mail your ballot or bring it to the elections office or to any worker at a polling place within your county of residence. Ballots received after the polls close on Election Day cannot be counted regardless of postmarks. Elections Code § 3017
If I request a vote-by-mail ballot, can I change my mind and
still vote at my regular polling place?
YES. You must bring your non-voted vote-by-mail ballot and give it to the
polling place worker before voting a regular ballot.
Elections Code § 3015
Can I give my voted vote-by-mail ballot to someone else to
return for me?
If you are ill, or have a physical disability, you may designate a spouse, child, parent, grandparent, grandchild, brother, sister or a person residing in the same household as the vote-by-mail-voter to return your voted ballot for you. Your designated person may return it in person to the election office or to a polling place in your county, or may place it in the mail for return to the elections official. Contact your county elections official for more information. Elections Code § 3017