It is calendar Days and not court days. That is how days are counted. So, a 3 day notice means you must pay rent in 3 days, or 4th day you can served with a UD. I hope this gives you some direction and insight on your question and I truly wish you the best of luck! As an aside, if you found my direction helpful, and if you feel appropriate; could you be so kind as to designate my answer as the “best” answer to your question?
See enclosed Landlord-Tenant Guide (specifically p. 67 start) which will hopefully shed some additional light on the topic: http://www.dca.ca.gov/publications/landlordbook...
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained. Please click "helpful" or "best answer" if my answer added any value or add a "comment" if you have more info for me to help you get a better answer.
Most common error is that the day of service is counted. Begin with the day following service so if a three day notice was served on June 1st the notice could expire on June 4th at the end of the day. One issue is when the notice expires on a weekend. If its a 3 day notice to pay or quit I find it best to wait out the following Monday. Though this is debated by attorneys especially if rent can be paid over the weekend. But I find waiting best practice to avoid the argument. It's always best to consult a lawyer. This should be used for general information and not considered legal advice.