"Schedule Task" is a Operating System component that provides the ability to schedule the launch of programs or scripts at pre-defined times or after specified time intervals.

For schedule a task login to your Plesk Control Panel, now click on Scheduled Tasks in the Additional Tools.

Now Select the System user under whom the scheduled task should be run and click Next.

 Click on Schedule New Task to Add a new task.

In Linux the system application "Crontab" manage the Schedule Tasks. If you want to schedule a PHP script run at 1.00 am every day, then you need to set the required value as below.

Minute : 00
Hour : 01
Day of the Month : *
Month : *
Day of the Week: *
Command : php -f /var/www/vhosts/yourdomain.com/httpdocs/folder/filename.php

Note:

• Need to calculate the time is 24 hours format, i.e. 0-24 hours. Example: 1 pm = 13:00.
• A field may be an asterisk (*), which always stands for "first-last".
• Ranges  of numbers are allowed.  Ranges are two numbers separated with a hyphen. The specified range is inclusive. For example, 8-11 for an "hours" entry specifies execution at hours 8, 9, 10 and 11.
• Lists are allowed. A list is a  set  of  numbers  (or  ranges)  separated  by  commas.   Examples:  "1,2,5,9", "0-4,8-12".
• Names can also be used for the "month" and "day of week" fields.  Use the first three letters of the particular day or month Examples: jan, feb, dec or mon, sat, tue, etc.  Ranges or lists of names are not allowed.
• Need to use the absolute path of the file, the default path is "/var/www/vhosts/yourdomain.com/httpdocs/". The syntex -f in php command specify the file you can use -q which run in quite mode.

Click OK to add the job.