Simple misting timer for Greenhouse 20 sec on, 20 min off

/*
  Greenhouse mist timer
  Turns on for 20 seconds, then off for remainder of 20 minutes,
  Action is echoed to the console if connected
*/
 
int led1 = 13,onoff=0;
long a=1;
//================================================

void setup() {     
  Serial.begin(9600);           
  pinMode(led1, OUTPUT); 
 }
//================================================

void loop() { 
  a++;  if (a>1200){ a=0;}  //count to 20 minutes
   if (a<20){               //20 seconds on
   if (onoff==0){
    onoff=1;   //toggle output to on if off
    Serial.println("Sprinkler on"); 
    digitalWrite(led1, HIGH);
   } Serial.print(a);Serial.print(",");  //show sprinkler time
   }
  else {
    
    if (onoff==1) {onoff=0;  //toggle output to off if it is on
    Serial.println(" ");Serial.println("Sprinkler off");
    digitalWrite(led1, LOW);} if ((a%60)==0){Serial.print(a/60);Serial.println(" Min");} }
  
 delay(1000);     //wait one second
}