Thank you for your reply.
Actually, now as I understand your question, what you describe would NOT be legal because an employer must ALWAYS pay at least minimum wage for all hours in which employees are "suffered or permitted to work," which includes all time in which an employee is under the control of their employer.If you are under the control fo your employer, you are entitled to be paid regardless of whether that time is billable to a client.
An employer can choose to pay minimum wage for such time but must specifically tell you that is what you will be earning, as noted above. If they try to simply "not pay you" for such hours without specifying that minimum wage shall apply, your ordinarily wage would apply and you would be entitled to pay at that rate for all such hours.
Nonpayment of wages for hours worked is a serious offense and one that the Labor Board takes seriously. An employer can't simply say "we aren't going to pay you because we didn't make any money off you." So, with regard to the hours worked without pay, an individual in your circumstance can file a claim with the Department of Labor Standards Enforcement.
To file a wage claim with the DLSE, visit this link: http://www.dir.ca.gov/dlse/howtofilewageclaim.htm
Again, I sincerely hope that this information helps you and I wish you the best. If I have answered your question, I would be very grateful for a positive rating of my service so that I may receive credit for assisting you.