(thanks for your comments, sorry about my delayed response)

>> You didn't give us enough information to answer this question well. >> 1. Like why can he only commit 1 full day per week, is it money, a bad time, he wants to see how the startup turns out before committing?

One reason is that he has some major responsibility of existing job. Also because currently the hardware part is relatively self-contained and has a smaller scope.

>> 2. Do you have money to pay him?

Not now, and probably not in near future.

>> 3. Do you need him?

Yes as of now. I don't have the skills required to design / build PCB.