Urgent help required for using Cron

Hi friends, I have to send mail to people automatically at specified time . Our environment is RedhatLinux 7.3 , Apache ,mysql and php. I am writing a program in php to send the mail if some Condition is met. I want to activate this program at specified time using cron facility. So, How can we do that? Can any one help me?. I have another problem also. We want Cron to indicate ( through a message or a mail) to us that a given task is completed or not. In the present case Cron does a task of sending a mail to a user. After sending the mail we want Cron to indicate to us that the mail was successfully sent or not sent. This we want to know through a program because we want to use this as a part of automation of sending mails. Thanking you, Siva