How to write If the player don't play the game for 24 hours, the game is over.

Hi. I make the virtual pet game.

And I want to make this : If the player don’t play game 24 hours, the game is over.

So what should I write code?

I already made the game over scene, “gameover”.

And here is my code that record the time while the player don’t play the game.

private void saveTime(){
    PlayerPrefs.SetString(ResumeKey, TimeUtil.GetUnixTime(System.DateTime.Now).ToString());
}

private long getResumeTime(){
    var lastPlayTime = long.Parse(PlayerPrefs.GetString(ResumeKey, "-1"));
    return lastPlayTime == -1 ? 0 : TimeUtil.GetUnixTime(System.DateTime.Now) - lastPlayTime;
}

void Start(){
    Debug.Log(getResumeTime());
}

void OnApplicationPause(bool pauseStatus) {
    if(pauseStatus){
        saveTime();
    } else {
        Debug.Log(getResumeTime());
    }
}

void OnApplicationQuit(){
    saveTime();
}

Upon login I would grab the computers date & time and check it against a txt file or database. Have it resave the current time & date after the check.