"as promised" / "when promised"

I know exactly when B&N lost me as a customer. Some years ago, to compete with Amazon, B&N began offering free same-day delivery in Manhattan if you placed your order over the Internet by 11 a.m. I did so several times – and not once did the books arrive [color=red]when promised. Everything I have ordered from Amazon has arrived on time or earlier. Then came Amazon’s game-changing Kindle, and instant delivery. Nothing I’ve read about B&N’s belated rival Nook has tempted me to try it.

Is [color=red]when, not “as,” fine?

“When promised” means at the promised delivery time.

“As promised” could mean that, but it could also mean other things at the same time or instead of that, such as in the promised condition, in the promised type of packaging, etc.

Thank you, Jamie.