[asterisk-users] Time counting down and # detect

[Pham Quy]

Hi all, 

What i want to do is something like karaoke. when caller call to
asterisk, a music song is played while caller sings. His or her voice
will be recorded and mixed with music. To do that i use MixMonitor().

But i enable user to select a part of song to be recorded (monitored) as
following: he press '*' to start recording. There are two way to stop
recording: he press '#'to stop recording or it will be stop
automatically after 60 seconds.

My question is: how can i implement counting down 60s?

ps: sorry for my english, thank you all for any help

Quyps