1. First, select Project-> in the menu bar; "Change working hours" option, as shown in the figure below, and then enter the next step.

2. Secondly, after completing the above steps, click the option of "New Calendar" in the pop-up "Change Working Time" dialog box, enter the calendar name in the pop-up "New Base Calendar" dialog box, then select "Copy Standard", press "OK" to return to the standard calendar, as shown in the following figure, and then proceed to the next step.

3. Then, after completing the above steps, switch to the "Work Week" tab, and then you can set a specific working period for each day of the week, as shown in the figure below, and then go to the next step.

4. Then, after completing the above steps, switch to the "Exception Date" tab, enter the national legal holiday date as the exception date in the project start time period, as shown in the following figure, and then proceed to the next step.

5. Finally, after completing the above steps, a green square will be displayed in the legend of the set exception date, as shown in the figure below. In this way, the problem is solved.