Currently The speed increases per frame after first 13 seconds. How to make it change the fall speed after each 13 seconds? I tried resetting the unscaled time but i think it doesnot work.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class speed : MonoBehaviour
{
    float clock;
    Rigidbody2D rb;
    // Start is called before the first frame update
    void Start()
    {
         rb = GetComponent<Rigidbody2D>();
         rb.drag = 5;
    }

    // Update is called once per frame
    void Update()
    {
          clock = Time.unscaledTime;
        //Debug.Log(clock);

          if (clock >= 13)
          {
            if(rb.drag > 0.1)
            {
                Dragreducer();
                clock = 0;
            }
            else
            {
                Gravityreducer();
                clock = 0;
            }
          }

    }
    void Dragreducer()
    {
        float percentageindex = 0.003f * 5;
        rb.drag -= percentageindex;
        Debug.Log("Drag " + rb.drag);
    }
    void Gravityreducer()
    {
        float percentageindexgravity = 0.003f * 1;
        rb.gravityScale += percentageindexgravity;
        Debug.Log("gravity " + rb.gravityScale);
    }
}

Maybe try clock += 1 * Time.deltaTime instead of clock = Time. unscaledTime