Purge Timer

Hello Everyone!

I have coded my own HUD and am wanting to create a purge. Me being a full noob at GLua I have no idea how to do this or start this. I will explain what I want to happen below but if anyone can help it would be amazing!

What I Want:

I want a timer to run on server startup where it counts down from 3 hours. Then when it hits for example 30 seconds left it would play a sound file (which I already have) and when it hits "0" on the timer I want the text to display "The Purge Is Now Active" then after 5 minutes of this Active State it would remake another 3 hour timer and repeat.