Definition
How long a muscle works during a set, which is the reps multiplied by the tempo.
Ten reps at 1-0-1-0 is about 20 seconds; the same ten at 3-1-1-0 is about 50.
TUT was once treated as the driver of muscle growth. The evidence now points at the hard reps near failure, and TUT is a byproduct of doing them. It stays useful as a constraint, forcing control with a slow tempo, and in rehab.
The trap is chasing seconds with light loads instead of adding weight. Load and reps still have to go up.