To disconnect your internet connection (dial-up / PPPoE) at a specified time, follow these steps:
Open Notepad and type this command line:
Save the file as “c:\disconnect.bat” (with quotes in order to avoid double-extensions)
Click Start, Run and type control schedtasks
Double-click Add Scheduled Task. The Scheduled Task Wizard starts.
Click Next. Under Click the program you want Windows to run, click Browse.
In the Select Program to Schedule dialog box, locate the file disconnect.bat in C:\
Click Open. Under Perform this task, specify a name for the task and how frequently you want this task to run, and then click Next.
Under Select the time and day you want this task to start, specify a start time and date for the task, and then click Next. Type the user name and password to run this task under, and then click Next. Click Finish.
For XP Pro, you can also use the Rasdial command with /disconnect parameter.