Interrupt condition not working

Projects Programming
7

Thanks @PickyBiker, I got it working with your solution. Also had to introduce some debounce code for the input.

Here's my final code for critique and / or assistance for anyone else with a similar situation. (PS, i still need to clean it up a bit and remove all the serialprint's I was using to assist with debugging.)

#define relayPin 2 // the pin relay is connected
#define triggerPin 3 // the pin where start switch is connected

long triggerTime = 0;
long duration = 300000;
volatile byte relayState;


void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);// initialize serial monitor with 9600 baud
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, LOW);
  pinMode(triggerPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(triggerPin), trigger, FALLING);
  Serial.println("Routine Begin");
}

void loop() {
  // put your main code here, to run repeatedly:
  if( (millis() - triggerTime) > duration && relayState == HIGH)
    {
      controlRelay();
      Serial.print("Time - ");
      Serial.println(millis() - triggerTime);
      triggerTime = 0;
    }
  else
    {
      delay(50);
    }
}// loop end

 void trigger()
 {
    static unsigned long last_interrupt_time = 0;
    unsigned long interrupt_time = millis();
    if (interrupt_time - last_interrupt_time > 300)
      {
        if(relayState == HIGH)
          {    
            controlRelay();
            Serial.println("Relay RESET");
            triggerTime = 0;
          }
        else
          {
            triggerTime = millis();
            controlRelay();
            Serial.print("Time - ");
            Serial.println(triggerTime / 1000); 
          }
      }
      last_interrupt_time = interrupt_time;  
 }// trigger end

 void controlRelay()
 {
    if(relayState == HIGH)
      {
        digitalWrite(relayPin, LOW);
        relayState = LOW;
        Serial.println("Relay OFF");
      }
    else
      {
        digitalWrite(relayPin, HIGH);
        relayState = HIGH;
        Serial.println("Relay ON");
      }
 }