can I run a web service on my site (asmx) in a preset time

Its for ASP.NET right? You would have to use JavaScript.

Following examples show auto refreshing the page but same technique can be used to refresh a list

http://forums.asp.net/p/1564306/3890239.aspx

http://geekswithblogs.net/willemf/archive/2005/10/30/58563.aspx

You can also use a timer

http://msdn.microsoft.com/en-us/library/system.web.ui.timer.aspx

I don't believe that this type of operation is appropriate for a web service.  JavaScript may work well for a web site, but not a web service.  Web Services are better at pull operations on demand.  I would look into some other type, like a Windows Service, or a scheduled task.

Which way round do you want this update to take place?

Scenario 1 : User loads a web page and part of the page requires regular updating with content from the same server (important distinction). Use something like Prototype's http://api.prototypejs.org/ajax/Ajax/PeriodicalUpdater/
Scenario 2 : User loads a web page and part of the page requires regular updating with content from a different server. Use something like Prototype's http://api.prototypejs.org/ajax/Ajax/PeriodicalUpdater/ but with a proxy running on your own server - You need to know about Same Origin Policy.
Scenario 3 : You have a database and you want to update a table with data from another website. Using your language of choice, create a script to pull the data and update the database.

Other scenarios will exist.

The scenario that I am targetting is:

On Friday @10:00 PM (server time), an operation in the web service starts automatically (unattended) without any user being on the site. The task will set the site in maintenance mode, and starts silently refreshing the site database from the XML exposed from another site, and after the database is refreshed, the site is set back to Working mode.

I am not interested in the operation itself, it is how to make it start on the server automatically. I would suppose that the server provider will not accept that I install a windows service to call the webservice operation, or to install an executable that I can ask for creating a scheduled job to run regularly. Thanks

You need to use the Task Scheduler running on some server set up to call the web service on the schedule you want. One example I use has the task scheduler run a PowerShell script that does the work.It helps if you can call the web service passing the parameters (in any) in the query string (GET vs. POST).

See File.ps1 script attached - schedule via task scheduler.

$url = 'http://www.webserver.com/FormGen.asmx/RunProcess?customerId=123&type=something'

$html = (New-Object net.webclient).DownloadString($url)

#Send-MailMessage -to yourself@gmail.com -Subject "test web service" -from yourself@gmail.com
    -BodyAsHtml $html -SmtpServer smtp.mailserver.com

exit

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gardavis

How to start powershel with windows interface. I want to Set -ExecutionPolicy RemoteSigned but I am getting an error (No parameter is known to be ExecutionPolicy), and when I try your powershell command it does not work because of the restricted ExecutionPolicy

Thanks