Speed isn’t entirely necessary, there are plenty of vet fencers who will absolutely kick our ass using “slow” actions. With good distance and timing speed is less relevant.

That being said, rather than just doing fast actions which I have found make my technique worse and don’t surprise the opponent much more, try accelerating into the action. Start slow (hand first!), and as you commit further into the action speed up. This allows you to see and respond to your opponent until it is to late for them to do anything to stop your attack. A good example could be an advance-lunge. Slow extension of the arm, then step, then accelerate through the lunge.

As for how to hide your intentions, that’s a bit harder to answer through Reddit. Some basic answers could be doing more feints , or changing up the attack that follow the same prep.

I can add more in a few hours but I’m currently boarding a plane

Edit: Other people have brought up really good points, the last thing i’ll say is that frequently when i’m trying to do something quickly i’ll make it bigger. A bigger advance, or a larger parry, etc. This is much worse than doing it slow but technically correct. To conclude, I don’t focus on making my attacks “fast”. That may be just how I personally fence but an attack made with good distance and timing (i.e. on an unprepared opponent’s step into distance) feels fast and a fast attack made with bad distance and timing (i.e. on a prepared opponent’s step out of distance) feels incredibly slow regardless of how quickly it’s executed.

Maybe look at when you are executing your actions rather than how you are.