. I know Cali is anything over 8hrs in one day is overtime but not in indiana. Which ot laws apply?

The overtime laws apply in the state you will be working. If you will be working in Ca., Ca. labor laws apply. (not In. where co. based)

Are you moving to California? Or are you just going on a business trip there? If the second, for how long?

business trip, 1 maybe 2 weeks

I have not been able to find any "bright line" documented about when California labor law kicks in for employees who are in the state for a short period of time only.

You could try calling the DLSE, but it's very hard to get through these days, I understand.

I am in agreement that this point could be more clearly spelled out. I have what is probably a good answer, but not one that you will like. CA is unusual in that all time spent working in state without exception is subject to CA taxes. And since CA does not support reciprocity, there is a good chance that the same wages will be taxed in both states. I think you could make a pretty good argument that if you are subject to CA taxes for work done in state that you are also subject to CA OT laws. The problem is do you really want to have to pay CA taxes in addition to your own state's taxes. This is one of those fairly complicated can's of worms that when you open it up, has unintended results.

A further complication is that I am citing an EDD publication (CA's IRS), while overtime is a function of DLSE (CA's DOL).

The following is from CA EDD publication 231-D.

Wages for Nonresidents
The wages a nonresident earns in California are subject to California PIT withholding. The amount of wages subject to California PIT withholding is that portion of the total number of working days employed within California to the total number of working days employed both within and without California.

Example
Assume there are ten working days within the pay period and a nonresident employee works six of those days in California and four days in New Mexico. California PIT withholding is required for 6/10 of the employee’s earnings for the pay period.

thanks for the replys