Yes, on the rare occasion I cook meat. Too unpracticed otherwise. I originally got one because I’m colorblind and was scared of undercooking red meat and tired of eating leather. As a bonus, I used it to get the temperature right when I got into fancier teas and inadvertently trained myself to judge the temperature of water pouring into my mug by the sound it makes within a couple °C, which is kinda neat. Now, if I could figure out how to do something similar so I stop overcooking food, that’d be grand…

Off during the day and between 17 and 20 °C when sleeping depending on the season.

Arsenic is a classic murder poison. It’s been known since anciemt times, though possibly unsuited to your onset requirement. Acute poisoning by ingestion is generally within a few hours, but if your character sustains lower doses over time, you could probably draw out the timeline to whatever you wanted. It would be obvious that the character is unwell during this time, but the symptoms aren’t super specific and could be confused with e.g. food poisoning.

Or just invent a mushroom like others said. The toxins are diverse enough that I doubt anyone would be too upset if you tuned it exactly to your timeline and desired symptoms.

Cyanide poisoning is famously pretty fast though…

What a coincidence, the end of my support for windows is also approaching.

jk I scrubbed that shit from my personal devices years ago after graduating.