With all the unknowns with taxing a French taxi from the Hertz drop off I decided to first attempt to go to the Swiss terminal and take a taxi from there. Ended up easy(once there!), here's what I experienced:

-Google doesn't seem to have the right info, I'd put in Hertz on French side specifically and of course it didn't take me there at all correctly. While I don't think it directed me there, basically it was in the direction of the Swiss Hertz drop off. Roads parallel each other so closely I think the navigation doesn't realize the actual road you are on. And since I never passed a border, I knew it was wrong. The swiss hertz agent put in the correct directions in google maps "Route Douaniere French Sector P20, Geneva...." Then although a few hiccups finally arrived to the right place. There's been a lot of construction and changes along this route and so google maps is a bit clueless getting you there. Kind of like anywhere in Europe in fact...

-Dropped off car, have to go to desk upstairs in terminal to drop off keys

-adjacent to the rental car desks is security for domestic French flights in that terminal. Between there and the check in desks you need to walk past that area and the door to enter the Swiss terminal is to the right slightly. Just inside is a border agent, he asked for boarding pass but accepted our reservation info for the next day as well(not yet check in time). No passport check even although I would imagine some would ask, this guy was mostly disinterested. And that's it, welcome to Switzerland! Out of the customs area and outside into a taxi.

-So for Swiss taxi ended up about $28. Took about 15 min back, no traffic as middle of the day.

So the datapoints about a next day reservation instead of border pass were correct and I can't imagine it would ever be different but who knows. If my reservation were further away than next day, I kind of think within 3-4 would probably even fly. Thanks again for the help.