In Los Angeles, the jails are severely overcrowded resulting in early release. No attorney can guarantee you will be released early but most of my clients with no violent offenses have been serving about 10 percent of their time. You may do up to your full sentence but there is a good chance you will do much less. Good luck!
The sheriff's are generally in charge of the credits someone will receive because they operate the jails. Depending on how crowded the jails get will determine whether or not they will be released early.