I'd assume the Tesla to have a lot better (quicker) reaction skills than you and you should probably just trust it (in this particular scenario) and relax, even though the distance might _feel_ too short.
It's weird because this really feels like one of the areas where technology could really excel in.
On my regular commute, the freeway interchanges that I must take, are too frequent, that I don't think the AutoPilot is worth the trouble to switch on. Especially when the freeway is empty, since I would have to take control of the car every few minutes.
The only scenario where I think AutoPilot is worth the effort to switch on, is if I must drive long distances on the same freeway, where you don't have to switch freeways. Like the drive from LA to SF. Or LA to Vegas. Or even just staying on the same freeway for 20 to 30 minutes.
I hope they can fix this deficiency. This AutoPilot technology is definitely beta, if they can't perfect simple stop-and-go freeway traffic.