Gantt chart not displaying details properly as per the time mentioned in datasource

I have followed all steps to create Gantt Chart on below link
https://docs.inductiveautomation.com/display/DOC80/Perspective+-+XY+Chart
but it is not displaying data correctly on graph as per the data in datasourse.Please find below screenshot in which for John time period is 8:00 - 10:00 but on graph its displaying different.Can anyone help me on this issue.