Questions about PowerUps?

The best way to do that would be to use Coroutines and WaitForSeconds.

Coroutines are enumerators that can be started by a MonoBehaviour, and are executed separately by the engine, on a frame-by-frame basis. A very convenient feature is the ability of Coroutines to suspend execution for a given amount of time, which is hands down the best way to deal with bonus duration and bonus cooldown.

So what you need to do is :

• Lock the power up when it is activated

• Increase speed

• Wait for X seconds

• Reset speed

• Wait for Y seconds

• Unlock the powerup

   using UnityEngine;
   using System.Collections;
   
   public class Player : MonoBehaviour
   {
       float m_Speed = 10f;
       float m_DefaultSpeedBonus = 10f;
       float m_DefaultPowerUpDuration = 5f;
       float m_DefaultPowerUpCooldown = 10f;
       bool m_PowerUpIsActivable = true;
   
       IEnumerator SpeedPowerUp(float bonus, float bonusDuration, float cooldown)
       {
           // Lock the PowerUp
           m_PowerUpIsActivable = false;
   
           // Activate the speed bonus
           m_Speed += bonus;
   
           // Let it last for bonusDuration seconds
           yield return new WaitForSeconds(bonusDuration);
           
           // Remove the speed bonus
           m_Speed -= bonus;
   
           // Start cooldown
           yield return new WaitForSeconds(cooldown);
  
           // After cooldown is over, unlock the PowerUp
           m_PowerUpIsActivable = true;
       }
   
       void OnTriggerEnter(Collider collider)
       {
           if (collider.CompareTag("PowerUp") && m_PowerUpIsActivable)
           {
               StartCoroutine(SpeedPowerUp(m_DefaultSpeedBonus, m_DefaultPowerUpDuration, m_DefaultPowerUpCooldown));
           }
       }
   }
  

You can apply the same logic to any PowerUp you want to implement.