If you then put in place the portfolio once more by borrowing $S_ t_1 $ at level $r$ you could realise a PnL at $t_2$ of $begingroup$ For a choice with price tag $C$, the P$&$L, with regard to changes from the underlying asset cost $S$ and volatility $sigma$, is https://www.youtube.com/watch?v=qMmsQ4kKgY4