What does 'tempo' mean in fencing, if it isn't just about being fast?
Tempo means timing: not how fast you move, but when you move. The rulebook defines one fencing time as the time it takes to perform one simple action, such as a step, an extension or a lunge. When a better fencer says it is about tempo, they mean they are reading your rhythm and choosing to act in the gaps: while your front foot is in the air, as you finish a step forward, or while your blade is busy searching for theirs. In those moments you cannot change direction, so even a slower attack lands.
In épée there is no right of way, so tempo is about arriving first by enough. Two hits only count as a double if the second lands within about 40 to 50 ms of the first. A stop hit 'in time' in épée means hitting into the opponent's preparation or attack early enough that their touch arrives after the lockout or misses, often to the hand or forearm as they reach forward. A counterattack made a moment too late is just a double, and one launched into a well-timed attack usually loses the touch.
In foil and sabre, 'in time' has an exact rule meaning. A stop hit normally has no priority against an attack. But against a compound attack, one built on feints, a stop hit is valid if it lands before the attacker has begun the final movement of the attack, which the rules describe as being one fencing time ahead. In practice that means hitting during a feint, not as the finishing lunge arrives. If it lands later, the referee gives the touch to the attacker.
To use tempo yourself, first make your own footwork harder to read: vary the length and speed of your steps, and mix in half steps and pauses. Then study the other fencer's rhythm. Many people advance in a steady one, two, one, two, and the moment their front foot lifts is your chance. A useful partner drill is for one fencer to advance and retreat freely while the other attacks only on the lift of the front foot. Start slowly with a coach calling the timing, then do it on your own.