There are 2 ways to solve this:
First is to plot in the actual hours instead of the points of the matrix that is holding the data, so, say your values are stored every second, instead of plotting
you should plot
and that would adjust the values of the x-axis.
The second way is to manipulate the values that are displayed on the x-axis, these are called the ticks and tick labels, for example:
So you can change the values of XTickLabel. I would suggest to try the first method and see if that works.
Hope this solves your problem.