From the "Multi-workout" widget (Samsung Health) I only have 2 exercises, Exercise Bike and Treadmill. When I click on Treadmill, a coundown starts, 3... 2... 1... and then you are presented with the "Exercise Screen". I call it that, so as not to confuse you with the term Watchface. The Exercise Screen looks identical to the Watchface called "Large" which is a large digital clock display.
The Exercise Screen however displays, calories burned on top, a stopwatch in the middle (largest of the 3 being displayed) and on the bottom displays your pulse info.
I was able to customize the Exercise Screen to display the current time in any of the 3 locations. After trying out various apps and wanting to start fresh, I "nuked" my watch to start fresh. Where do I go to make the necessary change? I hate having to exit out of the Exercise Screen to have to check the time while working out.
Just got off the phone with Customer Support. You have to add the Widget labeled "Exercise" on top and Samsung Health below. Once you have added the widget, there is an icon of a running man above a time frame like 1h 31m and a button named Workout on the very bottom. Click the Workout button, scroll to the exercise you wish to customize the Exercise Screen and click on the "cog" wheel icon. Scroll down to Workout screen and click on it. Finally, scroll down to either Screen 1 or Screen 2 and make your customizations.