grimwerk: I played the original Dungeon Master way back when. So when I started Grimrock, I was unsurprised by the heavy pause between movements. In fact, I'd been expecting it. I barely scraped by some of the early timed puzzles after many careful attempts, and the later timed puzzles were simply impossible. The problem was: Grimrock was running slowly, and I wasn't aware of it. Certainly, I thought, my computer is fast enough to handle what amounts to a hi-res Eye of the Beholder. (After all, I play The Witcher on decent settings...) Turns out, it was not. I reduced my settings and movement pace quickened. This gave me more leeway to complete the puzzles.

So if the timers are killing you, try reducing your settings, even thought that may seem unnecessary.

MadOverlord: I get around 20-30 fps typically, and I do the timed puzzles fine.
One thing I saw happen was someone tapping the movement keys repeatedly to move through a timed puzzle. If you hold a movement key down, it shouldn't even matter that much if your fps is low or not. The game will register it as constant movement.
Not sure how relevant that idea is, but it fixed one guy's problems with timing.