When you first ingest Belladonna, you roll a Fortitude save. Assume you failed, and are subject to the Belladonna affliction. So you use Extempore Effects to apply it as an effect on the character.
Extempore Effects applies an effect that shows you at Stage 1, with an expiration of 10 minutes
This is wrong - you don't start in Stage 1, because there's an Onset period before anything takes effect
Instead, there should be 4 phases (Onset, Stage 1, Stage 2, and Stage 3), and you should start at the Onset stage
When you advance the world clock by 10 minutes, the effect gets marked as Expired (and we'll assume that the system automation isn't set to auto-remove it). To continue tracking, you need to open up the sheet, and extend the duration by another 10 minutes (increasing it from 10 minutes to 20 minutes) to un-expire it. This is a bit unintuitive if you aren't used to re-activating Expired effects, which I was not. It's easy enough to roll saves and apply stage-based effects here, because they're right there in the effect sheet and easily clickable, but adjusting the duration and stages each time is slow.
I don't know if this is even possible, but generating the effect description with embedded macros that could be clicked to advance or roll back the stage would be helpful.
The macro to advance the stage would ideally increment the stage counter, and adjust the duration based on the new stage
The macro to roll back the stage would decrement the stage counter, and also adjust the duration
Both macros would ideally check if the maximum duration has been reached (respecting that time set in the Onset phase does not count towards the maximum), and refuse to extend the duration further if so (and notify of this)
In a test with Giant Centipede Venom, the initial duration set on the effect doesn't seem to match what's described in the Readme, and what I saw with Belladonna. As described, the initial duration is said to be set based on the duration of Stage 1 - but in this case, it applied a duration of 6 rounds. This is the maximum duration of Giant Centipede Venom, not the Stage 1 duration. Now, the max duration is MUCH more useful for injury poisons with single round stages, so I do prefer this - but it's a mismatch between description and reality.
Overall, the injury poisons in combat feel smoother than the longer term poisons.
when there's an onset stage, add "onset" as a stage (so it's: Onset, Stage 1, Stage 2..., and starts at Onset)
for long-term afflictions: add an extra "Advance stage forward" button to the description, which moves to the next stage and sets the duration to be that stage's duration. then another button that does the same but backwards (one step down). The effect should un-expire when this happens -- which might require me to change its start time in the data.
(I got those in a DM)