Source: Valve
It looks like Valve's prediction for the late February release date is accurate. The company announced the Steam Deck would go on sale beginning February 25. Those who have reservations will receive an email on that day, and they'll be given three days to place an order. The company plans to release new batches weekly, so it's best to keep an eye on your email.
Those who place their orders on the 25th will have their units shipped out on the 28th. You can still reserve the Steam Deck for US$5 if you haven't yet. But prepare for a bit of wait. The Verge reported the order page currently says you can expect to order "after Q2 2022."