Need to send SMS alert 15 minutes before start of appointment

I have an application in PHP that helps people fix appointments.

How could I code to send SMS's 15 minu开发者_运维知识库tes before the start of the meeting time?

I have code that takes care of sending SMS's. I just need to call the send method at the appropriate time.

Your best bet is making a script that sends an SMS to everyone who has a meeting in 15 minutes and set a cron job (or something similar if not on Unix) to run the script every 5 minutes or so.