Do something at a specific time

I want my program to do something at a specific time. This is what I have tried:

func rellotge() {
    countdownRellotge = Timer.scheduledTimer(timeInterval: 1,
                                             target: self,
                                             selector: #selector(actualitzaRellotge),
                                             userInfo: nil, repeats: true)
}
@objc func actualitzaRellotge() {
    let date = Date()
    let calendar = Calendar.current
    hour = calendar.component(.hour, from: date)
    minutes = calendar.component(.minute, from: date)
    seconds = calendar.component(.second, from: date)
    
    //print (minutes, ":", seconds)

    if (minutes == 40 && seconds == 0){
        print ("do something")
    }
}

This does not work if the computer goes to sleep. Even before that, it becomes buggy. (When I print the seconds, it seems that sometimes it skips some seconds)

How can I reliably make my program do something at a specific minute-second?