Some really good replies here. Basement Dweller and George had some great points.
I have played a bit with a 30 second shot clock which felt uncomfortably quick under pressure. What helped me was to establish my three checkpoints: 1) Decision (make up my mind, picture the shot I want, pre-shot routine, deep breath, air stroke, whatever), 2) Pause at cue ball at the end of my practice strokes as I connect with the shot, 3) Smooth start to my stroke.
This sounds too mechanical but I call it 'the waltz', because I think of it more as a 1-2-3 dance rhythm. Decide/connect/breath, practice strokes come to a pause, smooth stroke. Repeat. Repeat. I focus on the rhythm more than a to do list.
As for 30 seconds, for me where there was too much dead time was the deciding. I could spend a lot of time here thinking of different options and picking lint. What I learned is that I have 5-10 seconds to pick a shot, and as long as I pick a shot within that time frame I have plenty of time to complete the shot. In other words I don't have to speed everything up, I just have to speed up the picking a shot part, the rest can feel natural speed.
That is how Ralf Soquet and all of these guys play on a 30 second clock and look totally relaxed and even deliberate. They don't even rush their shot selection, they'll walk around and look at an angle, and they'll walk slowly and calmly. But you won't see them come to a standstill and stare either. It's just calmly look and decide, connect, stroke. 1, 2, 3. Very smooth.
So I agree that practicing quick can be beneficial, but we can speed things out by cutting out dead weight around decision making (and experimentally by cutting out some of the grind from our practice strokes). We don't want to rush our swings or add a bunch of nervous energy. Smooth, rhythmic, decisive, confident, natural. Roleplay like you were 100% confident in your natural game and play smoothly. I think this is spot on.