I looked for it a couple of days ago and had no luck. It seems the only option now is to enter your average sleep times. In the 3 days I've had it, the watch seems to do an OK job of recognizing when I'm asleep, even if its before or after the time I have saved in settings.
The only recent watches I've seen it on was the original vivoactive and the f3. They took it off the f3, but after complaints, put it back. (I'm not sure about the f3hr).
But it's not on any of the new Forerunners, the vivioactive-hr, etc., so I'd be a bit surprised if it is added to the f5 family. (the call to check it's state was also depreciated in Connect IQ - still there but going at some time)