I interpreted this as an ongoing effect. Since you could hold on to it for 4VP at game end, it is like saving 4 sparrows (assuming the correct tile was in the loading dock each time). Early game it will pay off handsomely. Late game it is worth 4VP. Mid-game -- depends.
However, I am not sure how you denote that you have this ongoing effect.
EDIT: I now disagree with myself. But I have no idea *when* you'd play that card.
Once you have acquired cards during the course of the game,you may play 1 hand card per round (at any time during your turn).
So clearly some of these cards will be played at different times during the turn. I can only assume that the cards must be played at the appropriate time during your turn, so the Patrician can be used once per game to choose a certain tile to place during the draw-a-tile phase.
The rules on first read seem to imply that you (1) draw and place a tile
(2) Do the appropriate actions
THEN (3) place a card (optional).
However, the wording of part 3 clearly states that a card can be placed once per turn perhaps during (1) or (2).