Countdown to the start of Rivian Deliveries - link is an active countdown timer
I am an optimist so I counted down to June 1st. Pessimists should add 30 days. Skeptics should add more than 30 days. I have an early R1S reservation, so I am hopeful for August 1st.
When you start backing up from the start of deliveries, things will move quickly:
85 Days until June 1st
55 Days or less Until Order Confirmation: It would seem that order confirmations would need to start at least 30 days before first delivery in order to plan production, allow for financing and possible trade-ins.
25 Days or less Until Test Drives / Hands On Access: Most of the reservation holders will want to at least have the ability to sit in and drive (or least be driven) in the vehicle before finalizing an order. To get reservations holders to a location to do this with time to decide on their final order, you need about 30 days to get the first groups through the process.
This is based upon my experience being one of the earliest Model X reservation holders. You can quibble over the exact timing, but any way you slice it, time is getting short with a lot information to dispense, hands on access to provide, orders to confirm, financing to secure, production to take place and deliveries to happen by June.
As a comparison, we waited years for our early Signature Model X reservation. But by this time before we took delivery (85 days before delivery), Tesla had released the details on the car, opened the online order system, held their launch party and given test rides.