New to programming and need some help

I have a project that I have completed what I originally wanted but now want to add to it.
It is running on a Arduino mini.
I have a Reef lighting controller (DIM4) that outputs a 0-10v analog dimming but my Led drivers are PWM.
I have the mini converting it for me and it works well.
so here is what I would like to add to it. I want a override button to toggle all lights on or all off for a fixed period of time.
here is the sketch for the conversion I am running but I need a nudge in the right direction for the override

// These constants won't change. They're used to give names
// to the pins used:
const int analogInPin1 = A0; // Analog input pin Ch.1
const int analogInPin2 = A1; // Analog input pin Ch.2
const int analogInPin3 = A2; // Analog input pin Ch.3
const int analogOutPin1 = 6; // Analog output pin that the Ch.1 is attached to 
const int analogOutPin2 = 10; // Analog output pin that the Ch.2 is attached to
const int analogOutPin3 = 11; // Analog output pin that the Ch.3 is attached to
const int lowerlimit = 90; // Any input below this value on inputs = 0 on outputs
const int upperlimit1 = 850; //Highest input value.. use to limit Max on Ch.1
const int upperlimit2 = 900; //Highest input value.. use to limit Max on Ch.2
const int upperlimit3 = 900; //Highest input value.. use to limit Max on Ch.3

int sensorValue1 = 0; // value read from input1 A0
int sensorValue2 = 0; // value read from input2 A1
int sensorValue3 = 0; // value read from input3 A2
int outputValue1 = 0; // value output to the PWM ch.1
int outputValue2 = 0; // value output to the PWM ch.2
int outputValue3 = 0; // value output to the PWM ch.3

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}

void loop() {
  // read the analog in value:
  sensorValue1 = analogRead(analogInPin1); 
  // map it to the range of the analog out:
  sensorValue1 = constrain(sensorValue1, lowerlimit, upperlimit1) ; //constrain the input to these values ch.1
  outputValue1 = map(sensorValue1, lowerlimit, 1023, 0, 255);  // change the analog out value1:
  analogWrite(analogOutPin1, outputValue1); // read the analog in value2:
  sensorValue2 = analogRead(analogInPin2);  // map it to the range of the analog out:
  sensorValue2 = constrain(sensorValue2, lowerlimit, upperlimit2) ; //constrain the input to these values ch.2
  outputValue2 = map(sensorValue2, lowerlimit, 1023, 0, 255);  // change the analog out value:
  analogWrite(analogOutPin2, outputValue2); // read the analog in value2:
  sensorValue3 = analogRead(analogInPin3);  // map it to the range of the analog out:
  sensorValue3 = constrain(sensorValue3, lowerlimit, upperlimit3) ; //constrain the input to these values ch.3
  outputValue3 = map(sensorValue3, lowerlimit  , 1023, 0, 255);  // change the analog out value: 
  analogWrite(analogOutPin3, outputValue3); // read the analog in value3:

 
  delay(500); 
}

The first thing to do is to get rid of the delay(). Then add code to read your buttons. When a button is pressed set the appropriate flag variable then, in loop(), if the flag is set do not execute the main code but force the outputs high or low as appropriate.

Use millis() to do your timing (see the BlinkWithoutDelay example in the IDE) which is the reason for getting rid of delay() in the first place. When the on or off time is over change the flag variable again and the program will revert to normal running.