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It's hard to say. Apple typically receives shipment on a daily basis. I don't think they receive shipments on a Sunday. When they receive shipments, they usually update the website for in-stock. It updates throughout the day. As far as I know, Apple Store set aside for walk-ins and have some set for online order in-store pick up. So just because apple.com shows that it's unavailable for pick up doesn't necessarily mean they are out of stock. So check the apple store to see if they have them.
 
I just saw a gold and blue 256 max pop up but only lasted for a few minutes. Hopefully a black one pops up soon😩
 
It seems random. I haven’t seen a proper restock since launch day morning but I see some pros popping up here and there. Haven’t seen any pro maxes near me which is what I’m looking for as well.
Here in California where I am, I see a lot of 13 Pros but absolutely no 13 Pro Maxes at any of the near stores.

I see Apple updated their site to make you type in your zip code now. My guess is the sites are being slammed with in stock requests.
 
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