This was the situation when South played the last ♣ from the dummy. He knew that East had 3 ♠ cards and 2 ♦ cards left. If I was South and saw East pitching a ♦ after thinking for a minute, I would be sure that he as not the ♦K, because everybody knows that you have to play a ♦ immediately if you are going to bare the king. First thinking and then baring the king is something normal club level players do, but not true experts. So I would faithfully cross to the hand in ♠ and take the ♦-finesse. If the finnesse fails because he has really bared the king after thinking about it, I would be really embarrassed and call the director because East, the expert, behaved like an ordinary player in order to fool me.
Apart from that, I really believe that the right to think whenever I have a bridge reason trumps all obligations not to mislead opps. Nowhere in the Laws it is mentioned that I have the obligation to take a thinking tank some tricks before the problem has fully evolved in order to avoid that opps are misled. I rather think that they still find a way to be misled if I think in advance.
Karl