Valve: "Customers will have 3 days from receipt of their order email to make their purchase".
After being delayed from the originally planned December 2021 release to a February 2022 one, people have been kind of worried that the production of Steam Deck won't go as well as they hope. However, Valve reassured us by confirming that everything is on track and Steam Deck "is still aiming for a February release".
Now we know they've kept their promise, as earlier Valve has announced, via a post, stating that "on February 25th, we will be sending out the first batch of order emails to reservation holders."
"Customers will have 3 days (72 hours) from receipt of their order email to make their purchase, before their reservation is released to the next person in the queue. The first units will be on their way to customers starting the 28th, and we plan to release new order email batches on a weekly cadence."
Valve also listed out a few additional details for those who are curious, which you can check from the link above.