HighStock Chart x-axis end point

Question

I have a series of JSON which starts at 8am and throughout the day it updates my graph as time goes by until 5pm. The problem is I do not want to return data from my api until 5pm. Instead I would like to set my graph to always have from 8am-5pm on the x-axis, I've played around with tickPositioner but to no avail.

So in summary this data displays fine:

{
  "d": [
    [
      1483689600000,
      7195.31
    ],
    [
      1483689900000,
      7188.45
    ],
    [
      1483690200000,
      7184.38
    ],
    [
      1483690500000,
      7185.82
    ]] }

But I do not want to have to return the following in my api [ 1483690500000, null ] etc etc for the remainder of the day, I just want to have the end time (5pm) being set in the javascript if this is possible?