PlaytimeTracker.cs

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

public class PlaytimeTracker : MonoBehaviour {
    public int heartbeatCount = 0;
    
    void Awake() {
        DontDestroyOnLoad(gameObject);
    }

    void Start() {
        StartCoroutine(PlayTimeHeartbeat());
    }
    
    IEnumerator PlayTimeHeartbeat() {
        while(true) {
            GoogleAnalytics.TrackEventWithValue("play_duration_heartbeat_seconds", "", heartbeatCount * 30);
            yield return new WaitForSeconds(30);
            heartbeatCount++;
        }
    }
}