It’s not that timing variation isn’t important, it’s just that suddenly moving much faster (or slower) can be a giveaway if it is centered around a move. As can suddenly stopping your patter to concentrate on replacing a card in the deck (I would think that’s a dead giveaway)

We should be conscious of changes in tempo, but use it purposefully to create interest rather than to hide a move. Yes?

If you’re doing an effect and it’s a part you really want them to focus on something, you may slow down, talk slower, be extra careful with the cards, showing how “fair” everything is. If you then relax (and kind speed up to your “normal” rate) at this moment, they relax as well. It could even have a comical effect.

We give things more attention, and therefore, usually slow down, when we deem it’s important to the spectator’s appreciation of the effect. When we want them to believe things are unimportant (when in fact, it may be the very method), I think it’s okay to speed up as long as it’s to your normal/everyday/natural speed.

I think the important thing is if you change your pace, don’t do so so abruptly, or have a reason (changing gears), or just make it natural. We’re not robots! Everything has a good context.

Clearly if you handle cards/coins/etc too fast or too slow at a certain moment it is a giveaway, but one thing I see a lot of new people fall prey too is slowing down their speech. Many magicians have to think so hard about the move, that they can’t continue pattering at the same speed, and the audience can tell that your mind must be preoccupied by a move because you stopped talking.

THis can be solved either by learning the sleight cold, so you can talk over it, or by scripting the magic so you don’t have to talk over moves that require a lot of mental effort.