I don't think there is such a rule. Example for a thinset may be: the day you mixed it and used it, it was too dry and warm. Also how slowly/quickly you work, therefore, your own experience. I also mix in some admix (milk) and this can make it feel like the grout or thinset dried too quickly. Using straight on a plywood/cement board can reduce the moisture quicker.
For the setting type joint compound you can use the old plaster trade method. Put water in your container then slowly sprinkle the setting compound into the water until all the water is absorbed. let stand about three mins. than mix by hand. ( DO NOT DUMP COMPOUND IN WATER ) Sprinkle it in.
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