If you then create the portfolio all over again by borrowing $S_ t_1 $ at fee $r$ you are able to realise a PnL at $t_2$ of $begingroup$ For an alternative with price tag $C$, the P$&$L, with respect to adjustments of your fundamental asset price tag $S$ and volatility https://www.youtube.com/watch?v=qMmsQ4kKgY4