Saying your project period ends soon gives me the impression that this is a student project, which are discouraged on LQ. While many of us will help with them, you need to what you have been trying and explain what it is that you are having trouble with. The important thing is to learn and understand how things work, not to be given an answer to submit which won't work once you finish school.
Here are some links to scripts and tutorials about how to send mail:
The first example is from the command line and you could write a small bash script to call the function. It is really deceptively simple. The second and third example, show how to perform the same function using Perl. The choice of language is really immaterial, as they call call /usr/bin/sendmail. Each of these will show you examples of how to solve the problem. Postfix provides a sendmail function.
As I stated earlier, I don't know of a way to get Postfix to perform the timing function. This is the realm of Cron. Attempting to use Postfix for this function would also be against the Linux philosophies of do one thing and do it well and designing your programs to be read from and provide output to another program. Cron, on the other hand knows timing and that is it's function, which it does well. Cron is designed to call a script on a periodic basis. It is the perfect tool for the job.