Hi Peter, 

can you elaborate your query.

If you want to schedule task automatically, 

The start and end dates for all tasks in the project are automatically scheduled based on the project start date and the calendars, constraints, and predecessors set on the tasks.

I am also including the answer to two common questions regarding dates below:

How to set a date to earlier than the project start date?

A task cannot start on a date earlier than the project start date. Please try adjusting the "Start Date" on the "Project Properties" dialog by clicking "Properties" in the "Project" menu of the Gantter editor.

How to set a date for a weekend?

You can have your project include weekends in the schedule by setting your Project's calendar to a calendar that includes weekends such as the "24-Hours" calendar. Please use the following steps:

1. Open the "Project Properties" dialog by clicking "Properties" in the "Project" menu of the Gantter editor

2. Set the "Calendar" field to "24-Hours"

3. Click the "Save" button on the bottom-right of the "Project Properties" dialog.

Calendars can be assigned to the project, tasks, and resources. Some calendars, by default, have every day as a working day such as the "24-Hours" calendar. Other calendars such as "Standard" have Monday-Friday as working days and Saturday and Sunday as non-working days.

Please see the help video which demonstrates how to set Working days to Non-Working days and Non-Working days to working days for a calendar.

Rather than setting for each particular day as shown in the videos, you can also set for every day by choosing the appropriate setting from the drop-down labeled "Working time setup" such as "All Sundays by default".