How do you manage the advance of a player on a project ?

Hi everyone, I wanted to know how do you manage one of your player working on something like a new recipe, potion or on the discovery of a ritual, something who will take several days. Usually i make them roll a D10 x skill's dices, 1 per day, but i want to make it more meaningful, something with a probable failure. So how do you manage a player making a project on several days?

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