Set Metronome Timer to play a sound precisely at every given interval (e.g.: 500 ms)

Question

I'm making an Metronome app. I wish to have it count precisely 4 beats in a loop with an accent on the first beat.

Inside Android Studio on my simulator it works fine, but on my actual phone (Galaxy J3 - 2018, Android v9) that time interval is not stable at all it's very random.

I have tried Threads, Coroutines, Handlers but nothing seems to work. I also had a look at the Timer objects, I was trying to copy someone's code on Stack Overflow and refactor it but without any success

This is my code so far (which works on the emulator)

timer = 5000
timeSignatureTop = 4
accentPlayed = false
measureCount = 1

Thread {


            while (!stopButtonPressed) {

                Log.d("Thread running", "running")

                if (!accentPlayed) {
                    mediaPlayerAccent!!.start()
                    measureCount++
                    accentPlayed = true
                }

                else if (measureCount < timeSignatureTop) {
                    mediaPlayerBeat!!.start()
                    measureCount++
                }

                else if (measureCount == timeSignatureTop) {
                    mediaPlayerBeat!!.start()
                    measureCount = 1
                    accentPlayed = false
                }

                Thread.sleep(timer.toLong())

            }

            Log.d("Thread stopped", "stopped")
            return@Thread

    }.start()