To send the message:
https://sampwiki.blast.hk/wiki/SendClientMessage
To format the message to look good:
https://sampwiki.blast.hk/wiki/Format
To calculate the amount of seconds:
http://en.wikipedia.org/wiki/Modulo_operation
(For some reason that Pawn language is not included into the list but it's still as many other languages "%".
Formula to calculate seconds: minutes % 60
Formula to calculate minutes: the variable used above which is to be a float for this to work.
I won't build the command because you will probably ask how to build it and then someone else will do the work for you. I have basically explained the basics, if you don't understand format I shall tell but otherwise I'm not gonna' build this for you buddy.