When you order tires from Costco, the earliest day you can schedule for installation is in 10 days. They need time to ship tires to your local Costco tire center.
When I ordered the tires for my Miata, the earliest available day for installation was Monday, March 15. But I wanted to schedule it several days earlier because I am scheduled for Costco shopping soon.
So, this is what I did.
I kept track of UPS tire shipping status. Also, Costco sent me an email notification when they received the tires. So I quickly called Costco and asked if they can find me an earlier date. Updating the schedule was painless and instantaneous. I refreshed the online appointment page and saw my updated schedule.
Now I can enjoy Costco shopping while they install my tires.