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