How can I tell how long a curio will take before I craft it?

[Dondy]

My credo quest told me to study a hand impression. Mousing over the recipe in the crafting menu informed me it would take eight hours to study. Once I made the thing it informs me it will take four days, twelve hours.

Why is there a difference?

What is the pattern to it, if there is one? For example would a crap q hand impression study faster than a higher q one?

It's not just hand impressions. I keep crafting different recipes that claim they can be studied in a certain amount of time and then find it takes more than three times as long when the items are actually made.

[abt79]

it's because the fired and unfired versions are different curios with different stats. The unfired version is actually slightly better.

Quality has no effect on study speed, currently

As for items studying ~three times faster than listed, that's because the tooltip shows study time in "game time" which passes a little over three times as fast as Real Life time (that is, the ingame day/night cycle completes one full rotation three times in a little under 24 RL hours).
The devs created "game time" and listed curio study time values in it because they're autistic and don't play, or have dedicated testers for, the game they made. They frankly don't care that it's annoying to have to divide all listed study times by three-ish, and in fact are probably highly amused that it frustrates you. I'd highly recommend using custom clients (such as Ender's) for this, and a multitude of other reasons that ultimately boil down to the developers caring more about form than function unless continually begged.

[shubla]

Divide by 3.29 to get the accurate number.