I'm surprised how long Costco lines are. And the savings is maybe 50 cents per gallon, or 15% off, but that little savings is enough to make a Costco gas station line longer than a Shell / Chevron gas station. For a full tank of around 15 gallons, it's only $7.5 savings, which may be enough for maybe one Chipotle entree.
And most the cars I see at Costco gas stations have BMW / Mercedes clients. Those people have the money for a Tesla but chose to not buy one, but still want to save money on gas and bypassed the opportunity to buy a Tesla which is much cheaper to drive and has better performance. Plus the opportunity to never have to stop at a gas station ever again for local driving. I feel some people won't give up gas cars even with all the benefits of EVs.
Assuming there are no lines at the Supercharger, it probably be the same amount of time as waiting at a Costco gas station.
I threw out the idea to my Tesla advisor about standing at a Costco gas station to give my referral code to all those customers. He said if I got all those Costco customers to buy a Tesla that Tesla probably hire me and pay me.