Score Multiplier by Time

Here is my score manager script I made:

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreManager : MonoBehaviour {

	public Text scoreText;

	public float scoreCount; // What the score is when the scene first loads. I set this as zero.

	public float pointsPerSecond; // Every second, the points increase by THIS amount. Right now it is 100.

	// Update is called once per frame
	void Update () {

		scoreCount += pointsPerSecond * Time.deltaTime;

		scoreText.text = "" + Mathf.Round (scoreCount); // It comes out as a float with like 6 decimals; I round to an nice, clean Integer 
	
	}
}

My problem that I cannot figure out how to solve is: How do I make a multiplier that increases the score by times 2 after 30 seconds of the game, then increases the score by times 3 after 1 minute, then times 4 after 1 Minute and 30 seconds, then finally, times 5 after 2 minutes?
Thanks

You could do something like this

private float scoreMultiplier = 1.0f;
private void Update()
{
    if (Time.timeSinceLevelLoad - lastTime >= 1.0f)
    {
        lastTime = Time.timeSinceLevelLoad;
        scoreMultiplier += Time.deltaTime / 30.0f;
        scoreCount += pointsPerSecond * scoreMultiplier;
    }
}