Plotting a 3D time space diagram but not getting the z axis correct

Hi,

I am plotting a 3D time space diagram through the 3D line graph option.

I have the latitude and longitude on x and y axis. I am plotting time on z axis which ranges from around 7:30 AM to 7:30 PM. However I cant get the z axis to spread evenly from morning to evening. Instead I am getting blocks of AM and PM along z axis. The plot is shown below. You can see the irregularity in z axis.