Edited the comment to include verification almost simultaneously with your post :)

But yeah, obviously as the transaction value goes up the merchant will need to wait a few more seconds to counter doublespend attacks.

>You must submit it to the network

Not necessarily true, ideally the customer doesn't need internet connection and just transmits the signed transaction to the PoS.

>and the merchant must be reasonably confident that it will be accepted in a block as-is and that the block will not be orphaned

First of which can be verified very fast by a computer. I believe orphaned blocks are rare enough that they're mostly a non-issue.

I guess it's important to point out that in practice most Bitcoin ATMs I've used did 0-confirmation transactions up to 1000 euros after only a few second wait, so it's not like all bitcoin merchants suck.

The average confirmation time for a Bitcoin transaction was 400+ minutes recently (and is still around an hour even now). https://blockchain.info/charts/avg-confirmation-time?daysAve...

Yes, but you don't need more than 20-30 seconds to be confident that a transaction isn't a doublespend attempt.

After that it's only about checking if the fee is high enough.

> After that it's only about checking if the fee is high enough.

Which can take up to 72 hours, right?

No, you just check if the fee per KB is more than x. Where x is a fee that is likely enough to confirm. This is practically instant.

I'm not sure "likely enough to confirm" is going to go over all that well with many merchants, particularly when that chart shows the price-per-byte jumps all over the place rapidly.