I just did a CSS guided test on the 945. It popped up a number when I saved the workout. But where do I see the result after? I poked around GC Web and the Connect app but it wasn't obvious to me where to find this.
The only place I found the results were on the watch in user settings. I hope Garmin eventually extends this feature to calculate swim zones and show graphs for time in zones, just like for cycling power zones.