Any time you then put in place the portfolio once again by borrowing $S_ t_1 $ at price $r$ you can realise a PnL at $t_2$ of $begingroup$ For an option with selling price $C$, the P$&$L, with respect to alterations of your underlying asset value $S$ and volatility $sigma$, https://www.youtube.com/watch?v=qMmsQ4kKgY4