IFAB Law 7.4 - On duration of match
If a penalty kick has to be taken or retaken, the half is extended until the penalty kick is completed.
IFAB Law 2 also states: "If at the end of the half, the referee leaves the field of play to go to the referee review area (RRA) or to instruct the players to return to the field of play, this does not prevent a decision being changed for an incident which occurred before the end of the half."
https://www.skysports.com/football/...runo-fernandes-goal-after-final-whistle-stood
OK fine I'm wrong but the prick was playing fergie time.