The defaults are based on published papers, but should be interpreted loosely given the variability. A few considerations:
1. Even though some companies list precise #s for caffeine content, actual caffeine content can vary widely from day to day (259mg - 564mg) according to [1]
2. Caffeine half life varies from person to person, from ~1.5 to ~9.5 hours. So 5 is typical according to [2], but unless you're a smoker or on certain birth control I haven't found anything yet to say which end of the distribution to expect for yourself.
3. Caffeine sensitivity also seems to vary from person to person. And the "sleep threshold" is more of an upper bounds than a target, based on working backwards to figure out how much caffeine subjects had in their system and still saw sleep disruption in [3,4,5]. So participants in [5] slept worse when you'd expect them to have ~25mg of caffeine remaining in their system on avg, but that doesn't necessarily mean they'd have slept normally at 24mg.
1. Even though some companies list precise #s for caffeine content, actual caffeine content can vary widely from day to day (259mg - 564mg) according to [1]
2. Caffeine half life varies from person to person, from ~1.5 to ~9.5 hours. So 5 is typical according to [2], but unless you're a smoker or on certain birth control I haven't found anything yet to say which end of the distribution to expect for yourself.
3. Caffeine sensitivity also seems to vary from person to person. And the "sleep threshold" is more of an upper bounds than a target, based on working backwards to figure out how much caffeine subjects had in their system and still saw sleep disruption in [3,4,5]. So participants in [5] slept worse when you'd expect them to have ~25mg of caffeine remaining in their system on avg, but that doesn't necessarily mean they'd have slept normally at 24mg.
These are covered in a bit more detail in the writeup: https://towardsdatascience.com/interactive-visualizing-caffe...
[1] https://doi.org/10.1093/jat/27.7.520
[2] https://www.ncbi.nlm.nih.gov/books/NBK223808/
[3] https://doi.org/10.5664/jcsm.3170
[4] https://doi.org/10.1111/j.1365-2869.2006.00518.x
[5] https://doi.org/10.1016/0006-8993(95)00040-W