Timing delays in builder, first trial in loop

Hi all, I have a builder experiment where the trial loop, which contains several fixed-duration (non-slip) routines, is triggered by a simulated key press from the scanner, as described here.

To clarify, should the 0time of the MRI run timecourse correspond to the start timestamp of the trigger screen (e.g., text_trigger.started) plus the reaction time of that triggered keypress (e.g. triggerkey.rt)?

Although the timing of the routines within the trial loop is pretty good (usually not off by more than 1-2 refreshes), the first routine of the first trial in the trial loop seems to be delayed from the above triggerscreen+trigger.rt by ~90ms and sometimes up to 150ms. I’ve uploaded a short dummy version that shows scene pictures where I’m still getting timing delays up to ~90ms for trial loop, and closer to ~50ms for the first trial in subsequent runs.

The first Fix routine just shows two images that are set to ‘constant’ so I’m trying to figure out what else I might do to improve timing-- I’ve tried preloading with ISI in my main script and this didn’t appear to change things. Perhaps there is something in my system that is slowing things down. Thanks!

(Win 10 / PsychoPy 2022.2.2 Standalone)