Wow...this is like a story idea I had awhile ago, that I have yet to write into a novel (like many of my story ideas XP)
But basically, I look at this scenario using a mathematical concept. Some functions are periodic (go through cycles of values), like the sine or cosine function. If we use y to represent time to the external world, and x to represent time for a specific person, for a normal person living a normal life, the function is y=x (linear increasing). For these two, their function is y=sin(x). We can think of the time that the guys see the device as y=0 (which corresponds to x=0, x=pi, x=2pi, x=3pi, etc), which increases until the time they touch the device, which we can think of as y=1 (which corresponds to x=pi/2, x=5pi/2, y=9pi/2, etc), at which point they get "sent back" (y decreases) to four hours before they find the device, which we can think of as y=-1 (corresponding to x=3pi/2, x=7pi/2, x=11pi/2, etc.). They then go forward in to y=0 ago and so on.
Actually, it's somewhat more complex...I would use the idea of "branches" in Complex Analysis...at least, that's what I use for my story. It involves applying this to a real/imaginary mapping (real on one axis, imaginary on another axis), creating a helix in time, and in this case, the nth branch would correspond to kiba/shino-n/4...but I'm not sure I can explain it in the length of one post...guess you'll just have to read my novel (once I write it, of course ;P).
But in truth, I don't really believe in time travel...I'm pretty sure it's been proven impossible XP...but it makes for good philosophical discussions .