After you then setup the portfolio once more by borrowing $S_ t_1 $ at amount $r$ you could realise a PnL at $t_2$ of $begingroup$ For a possibility with rate $C$, the P$&$L, with respect to changes of your underlying asset price tag $S$ and volatility $sigma$, is offered by https://www.youtube.com/watch?v=qMmsQ4kKgY4