Hi folks! I have the same problem too. The time is missing in the complications for sunrise/sunset, but also in both the solar and astronomy watch faces.
So far none of the below mentioned measures helped:
On the watch:
* Turning the watch on/off
* Switching watch faces
On the iPhone:
* Killing/restarting apps like Settings and Apple Watch on the iPhone
* Turning Wifi on/off on the iPhone
* Turning Location for Watch Faces on/off
Currently I am waiting for Apple Care to come back with a solution.
BTW I also noticed that it takes quite some time to update the weather glance or app in the "current location" setting for this reason. However this update seems to work, albeit with a significant time lag.