[Youice]

if I understood you right, then create a loop timer* contains the negative "what ever", or if you want it becomes less every second, just put the negative you want.

pawn Code:

forward LessTimer();
public LessTime()
{
    for(new i=0; i<MAX_PLAYERS; i++)
    {
        Seconds[i]-- //seconds will be -1 for all players
    }
    return 1;
}

OnGameModeInit()
{
    SetTimer("LessTime", 1000, true); 
   // every second LessTime will be re-called, you can just place *LessTime* underneath OnPlayerUpdate and remove that line ^^ 
    return 1;
}

This is just an example/tips may help you.