Generally it doesn't matter if you're a little late.
Call them and tell them
We never had a problem
Your reservation stays in the system up to 48 hours after your original pick up time. It's a good idea to call ahead & let them know you've been delayed, however - at this time of year fleets can be very tight and if you've reserved a specialty vehicle you don't want them canceling it & giving it to another customer's reservation
It doesn't matter
Always worth calling, even if you are going to be less than two hours late ... San Diego has plenty of vehicles so unlikely to be a problem.
They generally hold cars up to 2 hours before they cancel the rental reservation. However if you listed your flight number on reservation, Hertz usually knows of the delay. At least that was my experience (at Orlando airport)
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