Not to be too pessimistic, but there's no reason that there should only be one "Great Filter". There could easily be multiple astronomically improbable events barring interstellar civilizations from bearing fruition. It might be just as improbable for unicellular life to form as it is for unicellular life to beget multicellular life, so on and so forth.
The great filter exists at all times as cited by the fact that the longevity of a species does not guarantee their future survival. All life may die off at any time.
