At least two of the stories I have written involve time travel. In one there is a time machine called the Horologe. It works through the use of ectoplasm. If you've read my blog on Chief Loh's myspace page, you know that in my stories, ectoplasm acts as a medium between the spirit world and the physical. In the spirit world, time does not move linearly like it does here. There is also no spatial location in the spirit world. All time exists as one moment and all places exist as one point. If you use ectoplasm to enter into the spirit world, you can re-enter our universe at any time and/or place of your choosing with the Horologe.
A similar concept appears in Orson Scott Card's Ender's Game series, except they use an artificial intelligence to "pop" a metal box "Outside" and back into our universe. They only use this box for "faster than light" travel.
I mostly was inspired by Poltergeist, the way Carol Anne and her mother exited the spirit world covered in ectoplasm and fell out of thin air into their living room. It wasn't until I saw the pilot episode of Deep Space Nine, "The Emissary", that I made the connection about timelessness in the spirit world. Commander Sisco had to explain linear time to the beings in the wormhole near Bajor. From this I asked myself: if there is no time over there, then why would anything that was able to travel into the spirit world have to come back out at the same time they left? That's the sort of stuff a 15 year old nerd loses sleep over. To be honest, a 34 year old nerd still loses sleep over it sometimes. Just ask my wife, Kayla.