TBH, there has been a few cases of a preorder going live and it selling out in 24 hours, now given people need to be on the ball but I would at LEAST say a 72 hour window should suffice.
For example, my wife manages a gamestop, they randomly are able to start taking preorders on certain games. Heck, amazon etc had the care package for preorder before she even knew about it at her store. Crazy thing is, people came in that next day and were unable to take ANY preoders on them, her store literally has 0 care package preorders and is unable to even get any.
By lunch they had 12 of them on ebay.
I understand supply and demand and it makes business sense, but moral integrity it lacks.