I just called the customer service support number, and received an automated reply to leave my number and that I'd be called back within 24 hours. I live in Hong Kong. Can I make an appointment for a service rep to call me at an appropriate time?

I don't know if you can make an appointment for them to call you. You might try calling again during business hours.

The wait was long when I picked up at SFO, but finally additional help arrived.

I have been renting cars a lot for work I tried for rental at first it looks chip but at the end with all the addons it comes to same as others. At San Francisco airport I waited 1 hr to get my car that is reduces. I have gold membership with Hertz and it's free to sing up. Every time I land at a airport my car is ready and it's a 5 to 10 minutes tops I'm in a car.

I never tried it. I went through third party option