Hi. I know I used a system time stamp routine that one of the folks here on the forum sent me. It uses a string to show date and time and one can move it into the HMI or wherever you want in logic. I used it for an indicator when a process ran it's cycle and also when the cycle counts were reset.
Just taking a WAG, one could use a compare instruction to go true when the pressure equals or exceeds what you need it to be, which would then trigger a time stamp. Just a thought really early in the morning and I hope I've helped you.