Well... not actually "instant", but he could have though of 'faster' transactions.
When someone of his skills and imagination is on his path to create a decentralized digital currency, how is the transaction times are not given the most important thought process? I'm sure it isn't hard to imagine instant transactions in today's worls when email is the medium of daily communication which delivers messages in matter of seconds?
When Satoshi left, his work was not finished. You can tell by his last posts he intended to do much more.
https://bitcointalk.org/index.php?action=profile;u=3;sa=showPosts;start=0Then, he mysteriously vanished with his coins (and the alert keys).