We do time dilation whenever it'd be convenient - mixing up how fast time passes in one place as opposed to another - and you can mimic the effects of proper time travel to the future pretty well that way (but we wouldn't want to; we're immortal and have lots to do, so why miss the time in between when it's available?) Time travel to the past - we aren't touching. Way too much downside potential. If we need something like it, we can whip up custom planes and adjust participant memories; actual time travel is more dangerous, less customizable, and much more likely to erase things from existence. We haven't found any naturally occurring versions, but if we do we might be able to mine them for useful tested possibilities.