After 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 $begingroup$ Assuming that you're Doing the job for your financial institution, there are a few unique P&Ls based on the functionality/ use: This short https://www.youtube.com/watch?v=qMmsQ4kKgY4