Problems merging 2 codes (blinking light and dfplayer)

You need to record your startTime when the distance sensors first detects something which is when it is less than MIN_DISTANCE and not current active.

const byte led1 = 13;                 // LED pin NORMAL PIN2 BUT 13 FOR TEST
const byte trigger = 6;             // PIR sensor pin SENSOR REPLACED BY TRIGGER
const byte echo = 5;                // Pin to echo        //ADDED FROM DISTANCE CODE
bool isActivated = false;

#include "SoftwareSerial.h"
#include "DFRobotDFPlayerMini.h"
#include <PCM.h>                    //ADDED FROM DISTANCE CODE

#define MIN_DISTANCE 30             //ADDED FROM DISTANCE CODE



unsigned long responsetime;             //ADDED FROM DISTANCE CODE
unsigned long distance;                 //ADDED FROM DISTANCE CODE

SoftwareSerial mySoftwareSerial(10, 11); // RX, TX
DFRobotDFPlayerMini myDFPlayer;

const unsigned long pauseTime = 6000;   // how long between PIR detections
const unsigned long blinkTime = 100;    // how fast to blink led

unsigned long startTime; // time PIR triggered
unsigned long lastTime; // last time we toggled led

void setup() {
  delay (3000);             //DELAY TIME FOR DEVICE TO START UP TO AVOID ERRORS
  pinMode(led1, OUTPUT);      // set led pin as output
  pinMode(trigger, INPUT);    // set sensor pin as input  SENSOR REPLACED BY TRIGGER

  pinMode (trigger, OUTPUT);  //ADDED FROM DISTANCE CODE
  pinMode (echo, INPUT);      //ADDED FROM DISTANCE CODE
  pinMode (led1, OUTPUT);     //ADDED FROM DISTANCE CODE

  mySoftwareSerial.begin(9600);
  Serial.begin(115200);

  Serial.println(F("\nInitializing DFPlayer..."));

  //Use softwareSerial to communicate with MP3
  if (!myDFPlayer.begin(mySoftwareSerial)) {
    Serial.println(F("Unable to begin:"));
    Serial.println(F("1.Please recheck the connection!"));
    Serial.println(F("2.Please insert the SD card!"));
    while (true);
  }
  Serial.println(F("DFPlayer Mini online."));

  //Set volume value (From 0 to 30)
  myDFPlayer.volume(3);
}

void loop() {

  digitalWrite (trigger, HIGH); // We send a 10 microsecond pulse           //ADDED FROM DISTANCE CODE
  delayMicroseconds (10);                                                   //ADDED FROM DISTANCE CODE
  digitalWrite (trigger, LOW);                                              //ADDED FROM DISTANCE CODE
  responsetime = pulseIn (echo, HIGH); // And we wait for a pulse back      //ADDED FROM DISTANCE CODE
  distance = responsetime / 58; // Distance calculation in cm               //ADDED FROM DISTANCE CODE

  if (distance < MIN_DISTANCE  && isActivated == false) {
    // first detection of something
    isActivated = true;
    startTime = millis();
    Serial.println("Sensor Activated");
    Serial.println("DFPlayer Working...");
    myDFPlayer.play(1);
    digitalWrite (led1, HIGH);
  }

  if ( isActivated ) {
    // blink led
    if ( millis() - lastTime >= blinkTime ) {
      lastTime = millis();
      digitalWrite(led1, !digitalRead(led1));
    }

    // check if we have been active long enough
    if ( millis() - startTime >= pauseTime ) {
      isActivated = false; // force PIR to trigger again or not
    }
  }
}