Overtime cases are inherently factual and depend on a multitude of factors.
Federal (i.e., FLSA) and state laws may come into play and often provide overlapping relief which may greatly affect the course of action one might take in any given situation.
There are numerous sources of law regarding overtime pay many of which overlap, including federal statutes and regulations, state statutes and regulations (including wage orders). (see 29 USCA section 207; Code of Federal Regulations, 29 CFR § 541.0 et seq.; and California Labor Code section 510 et seq.).
Generally speaking, the basic rate for overtime is "time-and-a-half" the regular rate for any hours worked in excess of the statutory maximum, which is generally 40 hours in a week under federal and state law, but also over 8 hours per day per California law. Some exceptions exist.
Also, despite the overlap between federal and state overtime laws, there are also very real differences between California and federal overtime law as it relates to overtime pay. Under federal law, the FLSA requires an employer pay overtime only if the employee works more than 40 hours in a given work week - no regard is given to how many hours an employee works in any given day. But California specified employees are entitled to OT pay after working either 40 hours per week or eight hours in one day (with double-time if more than 12 hours are worked in any single day), and for working more than six days in any workweek.
Many employment practices may violate these laws, including but not limited to: 1) misclassifying "non-exempt" employees as "exempt"; 2) misclassifying employees as "independent contractors"; and 3) forcing employees to work "off the clock."
There is a great deal more to overtime law analysis and an attorney should be consulted in evaluating any claim.