-= Time.deltaTime doesn't decrease float over time?

I have this script and it should work but a small part doesn’t.

public IEnumerator Starttt()
{
    StartButtonONE.Play("StartButton"); //Animation for removing the start button.
    totalTextTOMIDDLE.Play("ToMiddle"); //Animation for moving the total seconds text.

    yield return new WaitForSeconds(1);

    totalSeconds -= Time.deltaTime;
}

The “totalSeconds” is sposed to decrease over time, but instead it is decrased by the value of Time.deltaTime.

public IEnumerator Starttt()
{
StartButtonONE.Play(“StartButton”); //Animation for removing the start button.
totalTextTOMIDDLE.Play(“ToMiddle”); //Animation for moving the total seconds text.
yield return new WaitForSeconds(1);
while(totalSeconds > 0)
{
yield return null;
totalSeconds -= Time.deltaTime;
}

 }