This information is not yet available in the API, but I've filed a ticket to have it added in a future release.
I don't know all of the ins and outs of how this information is managed, but I believe that the data is processed by the server and sleep times are calculated there and not on the device. If that's the case, it's not as simple as adding an API to return these values--we'd probably need to pull the data from Garmin Connect. I'm speculating a little at this point, but I'm hoping to set an expectation that it may not be a quick implementation. :)
I think this might be determined on the Garmin servers (Garmin Connect) as the sleep times are used to look at the movements during those times and look at the patterns. I haven't heard of any watches that have the info on the watch itself.
Has there ever been a statement from Garmin on where sleep data is processed (on the phone then uploaded or calculated on the server from raw movement data then results sent to phone)?
The phone only acts as a pass through for data. That's why you need a data connection for anything. And you can sync the data with GE, where no phone is even involved.
