Automated Processes

Hey everyone, I was wondering if someone could guide me in the right direction on how to do something. We're adding something to our employee database. We will be adding a field that tells how many days the employee is on guarantee(probation) for when they are first hired. So what we'd like to see happen is that a process runs at a specific time every day and checks to see if we should be notified if the guarantee period will expire soon. something like if today's date is (guarantee days) past the start date of them employee, an email reminder should be sent out. My question i guess is how to get the automated reminder process to happen. Thanks!, Marky