FIY, big fonts doesn't help in reading the code, quite the reverse. Fortunately, it is simple enough that's not a real problem.
I think you should read item 3 of the Technical FAQ. It should be relevant to your case.

      Thanks very much

it allowed me to solve my problem

General note: if you search countdown in the forum (or use the search on the Processing site, the answers from the old forum are still relevant), you will find other examples.

Yes I had already done

I have a concern,
the code that I wrote it based on the information you gave me works only on the first click.
Indeed, it actually displays the count of 5 seconds but when I click post, time is decremented from -1.
Thank you kindly help me again


int x=400, y =100;
boolean DisplayMessage;
int startTime ;
final int DISPLAY_DURATION = 0;
PFont hightech;
 
int time; //time
int minutes; int seconds;
int timeLimit=9 ; // countdown  time
 
void setup(){
  size(600, 400); 
  smooth();
}
 
void draw(){
  background(255);  
  if (DisplayMessage)  {
    countdown2();
    if( (seconds==DISPLAY_DURATION)){
            DisplayMessage = false;
    }
  }
  else{
    text(" ohh lalaaa",x+160-10,y+140);
  }
}
 
 void mousePressed(){
 DisplayMessage = true;
 }
 
void countdown2(){
 
hightech = loadFont("NiagaraSolid-Reg-48.vlw");
textFont(hightech,20);
startTime = millis();
time = timeLimit*1000 - millis();
minutes = seconds/60;
seconds =floor( time/1000 );
println((minutes) + "'" + (seconds) + "''" ); //stroke(0,0,255);
fill(255); rect(x+160-5,y+140,20,15); noFill(); //noStroke();
fill(0,0,255); stroke(0,0,255);
text((minutes) + "'" + (seconds) + "''", x+160-5,y+155);
noFill(); noStroke();   

}

I haven't tried to run your code, but I have some advices:
- don't do loadFont on each frame! Move the line to setup().
- you set startTime on each frame, perhaps you want to set it in mousePressed(). Although you don't seem to use it...
- you compute minutes with seconds but you compute seconds after it.
- millis() continue to count from the start of the sketch to its end. You should use startTime (as set as I said!) in the computation of time.