There are some general rules of thumb (though they are generalisations, some LOs have shorter/longer sleep cycles than average, so they don't always hold):
20min - pain/discomfort/overstimulation
30min - overtired
40-45min - UT, woke at sleep cycle transition and couldn't get back to sleep - can be developmental or very UT
1hr-1:20 - UT - close to the right amount of tired, as made it through the sleep cycle transition but a small increase should help lengthen the nap again
These rules tend to apply until you get to one nap where things change up again and are much more variable. Its great to watch you LO whilst they're younger and sleep needs are more predictable to see how they behave when UT/OT as that is often the best gauge when they're toddlers.
I'll have a conversation with the moderators and see what we think re: a sticky, I'm not sure if there is one.