Shipping time of custom MacBook Air M1

Hello,

I live in Brisbane, Queensland and am trying to buy a MacBook Air M1 with the base configuration, except the RAM is 16gb, not 8gb.

I think the issue shouldn't be restricted to Australia, but when I go to the checkout to buy this product, I seem to get contradictory information about shipping times:

It says 4 to 6 business days but the time range indicated in the blue box is clearly not 4 to 6 days.

I also would like to know if they have this configuration in store usually, as it is only one additional upgrade. The 512gb models with 8gb of RAM seem to be everywhere, but I'm not sure about the 256gb storage models with 16gb of RAM.

Thank you,

Blake