Send LED HIGH after "x" seconds

jdickinsonarduino:
Perhaps I really dont have an understanding of the }
i thought it's to execute whats after it as a whole?
before moving on to the next?

The brackets are for bunching relevant stuff together.

jdickinsonarduino:
I'm really new at this...

This is about a lot more than "Send LED HIGH after 'x' seconds" ? isn't it?
You have to approach this thing in steps.
This "one felled swoop" approach is not a winner.

I inserted some brackets where I thought they should go, but that's kind of hard to tell
So, it compiles, but I'm pretty sure that it's not what you figure.

int photocellPin = 0;// Photocell connected to analog pin 0
int photocellVal = A0; // define photocell variable
int pirVal = LOW;// motion sensor variable
int ledState = 0;//state of the led 
int minLight = 20;//min light threshold
int maxLight = 20;//max light threshold
//the time we give the sensor to calibrate (10-60 secs according to the datasheet)
int calibrationTime = 30;        

//the time when the sensor outputs a low impulse
unsigned long lowIn;
unsigned long refTime;
unsigned long trippoint;
const long threshold = 5000;
byte DET;
const byte pirPin = 2;

unsigned long pause = 5000UL;  

boolean lockLow = true;
boolean takeLowTime;  

//int pirPin = 2;    //the digital pin connected to the PIR sensor's output
int ledPin1 = 3;
int ledPin2 = 4;
int ledPin3 = 5;
int ledPin4 = 6;
int ledPin5 = 7;

void setup() 
{
  Serial.begin(9600);
  pinMode(photocellPin, INPUT);
  pinMode(pirPin, INPUT);
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  pinMode(ledPin3, OUTPUT);
  pinMode(ledPin4, OUTPUT);
  pinMode(ledPin5, OUTPUT);
  //give the sensor some time to calibrate
  Serial.print("calibrating sensor ");
  for(int i = 0; i < calibrationTime; i++)
  {
    Serial.print(".");
    delay(1000);
  }
  Serial.println(" done");
  Serial.println("SENSOR ACTIVE");
  delay(50);
}

void loop() 
{
  photocellVal = analogRead(photocellPin);
  pirVal = digitalRead(pirPin); 
  if (photocellVal < minLight && ledState == 0)
  {
    for(int fadeValue = 0 ; fadeValue <= 255; fadeValue +=5) 
    { 
      analogWrite(ledPin1, fadeValue);   
      delay(30);
    }
  }  
  DET = digitalRead(pirPin);
  if (DET == 1)  // inactive
  {
    refTime = millis();
    trippoint = refTime;
  }
  else   // Active Low
  {
    pirActive(); 
  }

  digitalWrite(ledPin4, HIGH);
  digitalWrite(ledPin5, HIGH);

  if(lockLow)   //  IF without a Condition to Meet -- WRONG
  {  
    lockLow = false;            
    Serial.println("---");
    Serial.print("motion detected at ");
    Serial.print(millis()/1000);
    Serial.println(" sec"); 
    delay(50);
  }         
  takeLowTime = true;                   
    
  if(pirVal == LOW)
  {   
    digitalWrite(ledPin1, LOW);  //the led visualizes the sensors output pin state
    digitalWrite(ledPin2, LOW);
    digitalWrite(ledPin3, LOW);
    digitalWrite(ledPin4, LOW);
    digitalWrite(ledPin5, LOW);
  }
           
  if(takeLowTime)    //  another IF without a CONDITION!!!!!
  {
    lowIn = millis();          //save the time of the transition from high to LOW
    takeLowTime = false;       //make sure this is only done at the start of a LOW phase
  }
  
  if(!lockLow && millis() - lowIn > pause)  //  BAD code, and NO CONDITION !!!!
  {  
    lockLow = true;                        
    Serial.print("motion ended at ");      //output
    Serial.print((millis() - pause)/1000);
    Serial.println(" sec");
    delay(50);
  }
}   
    
void pirActive ()
{
  trippoint = millis();
  if ((trippoint-refTime) > threshold)
  {
    digitalWrite(ledPin2,HIGH);
    digitalWrite(ledPin3, HIGH);
  }
}

I removed a lot of the comments, that's the only way I could keep from flying into a rage.
You have a few IF statements without a Condition, the equivalent of: IF (B). Well, What about "B", anyway?
If (B == 100) or If (B == false) gives "B" a condition to meet. See?
Work out simpler stuff first that you can incorporate later.
There's much for you to develop.