There is nothing directly built in to do this. You can have a dialog box that popup on a timer and then you could check for the user that is logged in to the software and then display the alert only on that users computer that they are logged in on. The filemaker Training material has the reminder example in one of their lessons. You would just extent this example to check user logged in. The Training Material is excellant and can be download after purchase.
Thank you very much :). Will try that. Hope it's useful. :D