And ... how will you make a sound conclusion without proves?
Moz is right. IF there was an actual 'time slip', then the clock's in the car's ( and digital watches ) would reflect the 1 hour difference - not just the cell phones.
With a vehicle traveling from one side of a mountain, through a tunnel, to the other side of the mountain, seems reasonable that the signal would switch to a different tower. The time difference, as seen in the cell phones, also could be an issue caused when the signals of the two towers are interacting with each other inside the tunnel.
Time Zone difference doesn't work though, there is only one time zone in China.
IF there is a geological effect, as with a large deposit of magnetite, and mechanical clocks
are affected, still doesn't prove that a 'time slip' exists.
Admittedly, everything I presented above are guesses.
The only way I could make the best guess would be to travel to the tunnel in China ( wee, fun, NOT ) and conduct various experiments . However, since there are too many reasonable explanations on the table, unless one has an lots of money and free time, is it worth the trip ?
Anybody find this tunnel on google maps ? I looked and couldn't find it.