A priority date is the position you have on line, the visa bulletin states what application they are processing based on available visa numbers according to the date you filed your application- the priority date.
Processing times is how long a USCIS office or other government agency takes to actually process an application.
"Processing time" is a rough estimate as to when the USCIS will get around to looking at a particular type of petition or application. For example, in your case the California Service Center is taking about 25 months to review and adjudicate an I-130 Petition in your particular immigrant visa preference category. Porcessing time has nothing to do with visa availability.
On the othe hand, the Visa Bulletin is isuued by the Department of State, not USCIS. The Visa Bulletin lists visa availability by cut-off date. Simply put, if you are applying under an approved family-based petition with a priority date earlier than the cut-off date shown in your preference category, a visa is available.
I hope that clears things up a bit for you. Good luck!
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. A consultation with an experienced attorney is always the best way to go.
Processing time: The time it takes USCIS to process a form, assuming the priority date is current, or there is no applicable priority date.
Priority date: Your place in line for immigrant categories, based on filing date and demand in that category.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.