For GODs sake this request make no sense at all.
Lets think logically: first 'the coder' creates a nvault system saving players played time (ex. Alka's or Gizmo's plugin)
You add the "block low hour acounts" system in it and put it on your server.
Then the "blha" system would ban every single player 'cause you've just uploaded it on your own server.
You'd better make your server private rather then requesting this. or you should put the 'played time' plugin as soon as you open your server and then 'the coder' could do something for ya.