Swift: stop speech recognition after x seconds of silence

I've looked for a solution, but all of the ones I've seen are confusing so I thought I'd create a new question.

I'm using the speech library and I want the recognition task to stop after 2 seconds without input from the user. I know I want to use a timer, but I'm having trouble figuring out where to put it and how to update it.

I start the timer when the record button is pressed and I invalidate it when the stop recording button is pressed.

But where do I check if the user added new input? I was thinking of saving the last transcription and comparing it to the next one: when they are different, reset the timer.

Here's what my code looks like:

recognitionTask = speechRecognizer.recognitionTask(with: recognitionRequest) { result, error in
    var isFinal = false

    if let result = result {
        self.textView.text = result.bestTranscription.formattedString
    // Should I compare the result here to see if it changed?
        isFinal = result.isFinal
    }

    // Or should I do it here? In what order is this code even running?

    if error != nil || isFinal {
        self.result = self.textView.text

        self.audioEngine.stop()
        inputNode.removeTap(onBus: 0)

        self.recognitionRequest = nil
        self.recognitionTask = nil

        self.recordButton.isEnabled = true
        self.recordButton.setTitle("Start Recording", for: [])
    }
}