How to Schedule IISreset at specific time on powershell without manual intervention?

I'd just use a scheduled task.

What Mike said, just use Task Scheduler to run the command IISRESET /RESTART and whatever intervals you would like and that should be it.

Now keep in mind if this is a public facing web server or even a internal web server, to choose a time, that has no users.

hi,

make powershell script and put it in scheduled tasks in system

script look like 

Restart-Service W3SVC,WAS -force

and have extansion .ps1 , also check box wfor running it with highest privelegues and don't requiered you logged on.