my theory its in the 20th century (late 90s).
we've seen TVs before in the anime, we've seen electricity cables, we've seen medical machines in the hospital, we've also see a lot of technology in laboratories (orochimaru labs)..etc.
and chapter 700 time-skipped to the 21st century where now its not hard to find a thin lap-top....
It's just my thoughts I might be Completely wrong.