Quiz Timer

I’m doing a flash for a quiz competition. This flash will be use by the quiz master to show the questions with scores and timer.

For the timer, the quiz master will have buttons that shows 30 secs, 20 secs, and 10 secs. Each round of the game has different time, so the quiz master will choose the time. The timer will have a ticking sound and when it finish something buzz sound goes off.

How do you create this type of timer?

I have searched everywhere but most of it is about counting down to days, hours and do not specify the use of buttons to trigger the time. If anyone cares to show me how to I greatly appreciate it. Please help me I have a week to complete this project.