It would be both beneficial and excellent to not only have clients track the time they're doing a specific exercise but also the reps and load they are using during interval training, instead of waiting until the end and possibly remembering and recording wrong data or breaking the flow of the training to constantly pause and record only to transfer the data later.
This would help trainers support and display to our clients the true progress they are making within a given routine or with specific exercises in regards to strength, endurance, and even cardio vascular fitness.