No, I'm afraid that a decision in those circumstances is invalid. The best approach is to anticipate such problems by agreeing rules for delegating decisions to the clerk. No councillor can make a decision except in a properly arranged council meeting, but the clerk can make a decision at any time, although it must be one they have been authorised to make by a council decision. It's sensible to set limits and circumstances for the clerk's discretion, bearing in mind local circumstances, and have the clerk report any delegated decisions at the next council meeting.