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How to specify the end of a stimulus/stimulus transition using the frameN coding

OS (e.g. Win10): Win 10
PsychoPy version (e.g. 1.84.x): 3.2.3
Standard Standalone? (y/n) y
What are you trying to achieve?: exact timing in visual masked priming

I am having a rather simple question on how to interpret the timing of visual stimuli
using the frameN type of timing scheduling for a masked priming study.
In mathematic notation, the question is whether I should interpret the endframe of
a stimulus as including or excluding (i.e., [startFrame, endFrame] vs. [startFrame, endFrame[ )

So, on a 60Hz Screen I want a 500 ms forward mask, 50 ms prime and 500 ms target
and I am not sure how to set the transitions,
that is should they be overlapping or non-overlapping,

Forward Mask: start: frame 1 duration: 30 (= 500ms at 60Hz)
Prime: start: frame 30 duration duration 3 (= 50ms)
Target: frame 33 duration: 30 (500 ms)

or Non-overlapping
Forward Mask: start frame 1 duration 29 (= 500ms at 60Hz)
Prime: start frame 30 duration 2 (= 50ms)
Target: frame 33 duration: 29 (= 500ms)

I fear this is a duplicate question, but I could not find it on a search

thanks for any help in advance,
Holger Mitterer