I dislike Shadow Time Tricks.
It might be my general dislike for Time Travel stories, but the whole slow-time/fast-time Shadow stuff gets under my skin because I so rarely see it being used as anything but a player-initiated manipulation of the GM's good sense. You know, "game-breaking" stuff.
Now, it doesn't bother me that some Shadows may be slower or faster than Amber. It's the flitting about and pitting them against each other that disturbs me. It's like saying, "Hi, I'll put this plot point in storage, and take this one and get rid of it by accelerating it, and..." which is not necessarily anything bad, but it's a slippery slope. You expect me as GM to provide you with the challenges you enjoy...I expect you to twist the universe into knots. I think it's only fair that you offer me something a little less drastic than a Gordian solution.
With that in mind, there are Fast and Slow time shadows in my campaigns, but there's a catch: the Patternwalker metabolism is set to Amber (Pattern) Time. Too much time difference makes a Patternwalker physically ill. I don't think it'll kill them (for one reason, PCs follow the laws of Dramatic Effect, and it's hard to say, "You die in your bed because your body has slowed down too much. Make a new character," with a straight face.) It could work for a plot point: "You're ill enough that you cannot make it through a Trump. Someone will have to carry you through Shadow."
It can certainly make communications between Shadows wonky, and finding the significant difference of "Time" as a basic power initiate is a tricky subject at best.
Add in the entropy factor; when you bring something of a faster-timed Shadow into someplace slower, that item will tend to decay faster, maybe even on a higher ratio due to the Shadow "disturbance."
I figure that gives me some basic, but fair guidelines for players.