How much time off or rest must an employee have between shifts in the
state of california?

15. Are there any required rest times between work shifts -- i.e. an
employee works from 7:00 a. m. to 7:00 p.m. -- how soon can this
employee be called back?

There is no limit on when an employee can or cannot be called back to
work. Employers are cautioned, however, to keep in mind safety
concerns for employees to avoid injuries due to fatigue.

from site 
http://66.102.7.104/search?q=cache:otAahn_JpUoJ:www.dir.ca.gov/DIRNews/1997/otfaq.html+time+off+or+rest+must+an+employee+have+between+shifts++site:.gov+california&hl=en

Here are the numbers for the D L S E (Department of Labor Standards Enforcement)
From the same site. They can answer your questions regarding California Labor law.



Cities Telephone Numbers  
San Francisco 415-557-7878 
Sacramento 916-323-4920 
Los Angeles 213-620-6330 
San Diego 619-467-3002