Binary counter, button problem

Projects General Guidance
24

Alright, so I figured it out in the end, thank you to everyone who helped!
Here is the final code:

#include "funshield.h"
//setting up
constexpr int ledPins[] { led1_pin, led2_pin, led3_pin, led4_pin };
constexpr int ledPinsCount = sizeof(ledPins) / sizeof(ledPins[0]);
constexpr int Button1 = button1_pin;
constexpr int Button2 = button2_pin;
constexpr int activationDelay = 1000;
constexpr int periodicDelay = 300;

unsigned long lastTime = 0;
unsigned long lastTime2 = 0;
bool firsttime = true;
bool firsttime2 = true;
int counter = 0;
bool wasDown = false;
bool wasDown2 = false;
int isDown = 0;
int isDown2 = 0;

//Binary counter
void BN(int number, const int leds[], int ledsCount)
{
  for (int i = ledsCount - 1; i >= 0; --i) {
    bool currentBit = number & 1;
    digitalWrite(leds[i], currentBit ? ON : OFF);
    number = number >> 1;
  }
}
//Smart function
void TheThing(int Button) {
  if (Button == Button1) {
    counter = (counter + 1) % 16;
    BN(counter, ledPins, ledPinsCount);
  }
  if (Button == button2) {
    counter = (counter - 1) % 16;
    BN(counter, ledPins, ledPinsCount);
  }
}

void setup() {
  for (int i = 0; i < ledPinsCount; ++i) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], OFF);
  }
  pinMode(button1_pin, INPUT);
  pinMode(button2_pin, INPUT);
}

void loop()

{
  isDown = digitalRead(button1_pin);
  isDown2 = digitalRead(button2_pin);
  unsigned long times = millis();
  //Button1 pressed and first loop it is being held
  if (isDown == ON && firsttime == true) {
    if (times - lastTime >= activationDelay) {
      TheThing(Button1);
      firsttime = false;
      lastTime = times;
    }
  }
  //Button1 pressed and not first loop it is being held
  if (isDown == ON && firsttime == false) {
    if (times - lastTime >= periodicDelay) {
      TheThing(Button1);
      lastTime = times;
    }
  }
  //Button1 stopped being pressed
  if (isDown == OFF) {
    firsttime = true;
    lastTime = times;
  }
  //Button2 pressed and first loop it is being held
  if (isDown2 == ON && firsttime2 == true) {
    if (times - lastTime2 >= activationDelay) {
      TheThing(Button2);
      firsttime2 = false;
      lastTime2 = times;
    }
  }
  //Button2 pressed and not first loop it is being held
  if (isDown2 == ON && firsttime2 == false) {
    if (times - lastTime2 >= periodicDelay) {
      TheThing(Button2);
      lastTime2 = times;
    }
  }
  //Button2 stopped being pressed
  if (isDown2 == OFF ) {
    firsttime2 = true;
    lastTime2 = times;
  }
  //Button1 changed states
  if (wasDown != isDown) {
    //Button1 currently down
    if (isDown == ON) {
      TheThing(Button1);
    }
    wasDown = isDown;
  }
  //Button2 changed states
  if (wasDown2 != isDown2) {
    //Button2 currently down
    if (isDown2 == ON) {
      TheThing(Button2);
    }
    wasDown2 = isDown2;
  }
}

If anyone has any tips or ideas, feel free to share!
For now I will enjoy the fact that I managed it.