[Jack gets a politely skeptical look because being really careful doesn't seem like enough of a precaution when time is involved. He is saved from attempting to articulate that sentiment in a kind way by the prospect of looking at an actual time travel device.]
This is much more convenient than a TARDIS. [He and a Doctor had a rather nice conversation about the TARDIS long, long ago in another universe. Chekov hesitantly moves closer to inspect the wrist band, curious but trying not to be too invasive or pushy.] Does this generate closed time-like curves? Not here, I mean--I think the wardens must frown upon such things--but in your universe?