Expected-time on physical device

[andreareginato]

Think about returning the expected time to apply the change in seconds when a physical connection exists. This is not so easy because it could be pretty easy for functions, but for properties and complex functions the possible combinations could influence a lot the time for the executions. Here an example of what to send in the header.

X-Expected-Time: 0.5

[andreareginato]

Actually we could do something like this.

1. The device has completed the request and you are done.
2. The device will need some time to complete the request and sends you back the expected time.