Hello, I am traveling to San Francisco in February, and I wanted to know if I could pick up the car at any time, for example at 12 am (local San Francisco time)?

Priceline.com is also a good option

Go through Rentalcars.com and make a reservation there. It will be cheaper to do like that and they usually include insurance into the price and an additional driver as well. Alamo has very good prices on Rentalcars.com and better services compare to Dollar or Budget from my own experience.