When to add plum purée?

Hello I am going to brew this recipe from Chop&brew website it call Ice cutter winter warmer. Well my question about this recipe it say to add plum purée at about (1.020-1.024) in fermentation. Now I know one going to have to take hydrometer samples to determine where the 1.020-1.024 is but what a Rough estimate in how many days should I wait before I start taking samples again I know thing’s like fermentation temp,pitching rate, etc play a big roll ?

You may want to check 3 days into it… if its ale… Sneezles61