We do not have enough data on this route to provide a reliable graph showing how many days before departure it is the best to book.
However, usually the closer it is to the departure, the more expensive the tickets are.
There is no direct flight on the route from Reno Tahoe to San Diego Intl Airport
The shortest flights with a change last approx. 5h 56min.
Reno (NV) San Diego (CA)