Has anyone experienced slow save times on a sandbox account before via a Restlet? Seems to run fine until the actual save and takes around 16 seconds on a Sales Order. (EU West data centre)

Absolutely. I had an integration I was testing in Sandbox fail 90% of the time because of the latency. I had to persuade them to let it pass testing. Production did not have this issue.

Ah okay - thanks for letting me know! I was sticking Date.now() debugs everywhere to measure the time to find any code smells 😄