Duration and Lap button in workout builder should create 2 steps
When filling in a duration and the option lap-button in a workout builder step should create two steps on your Garmin device. In this way you can fort example have for a warming-up a minimum duration, like say 30 minutes. And if you are not in the correct place to execute the rest of the workout you still continue the warming-up till you get on the correct route to execute the workout. In this way you don't need to pause the workout on your Garmin.
Now the suggested duration by my trainer doesn't show on my Garmin.