The Start time, End time and the time slot difference can be set by following these steps:
Click on the Settings option from the menu and click on All Settings.
Under Configuration, select System Configuration.
Go to the Dispatch Board Setup.
Scroll down, under Define Time for Dispatch Board you will see the following:
This option will allow you to set the start and end time for your dispatch calendar as per your working hours. You can also set the time slot difference in minutes.
Once done, click on Save.