Shipping confusion, dishonest shipping times and Auto-cancellation?

Hi all.

I've used Aliexpress to purchase little things with Choice shipping and have never had an issue. Stuff ships almost immediately and arrives on time.

I'm now trying to buy a computer case and although it says it's in stock and will arrive by the 21st of January, the buyer messaged me and said it will take 20 days before shipped. I asked to cancel, they try to convince me not to and ultimately they cancel as do I.

I buy from another seller. They say something similar, that it will take 15 days to ship. But in looking at the order, it says if the item is not shipped within 7 days, an auto-fund will be made.

What's the catch here? Come 7 days from now, seller will ask me to extend time? Am I missing something?

Thank you.