Generally anything shipped should contain @20% water.
That said, clay materials will make a slight difference in "ready" time, but they all should roughly fall into the same "window" of readyness. Where porcelain on the early end may bend a little, and grogged stoneware may be a little dry, which makes more mess when scoring. But everything in this window can be used to make a useable product.
The safest, most consistent, and efficient way to get to this window is simply the material you are working on.
Since Plaster and Drywall both wreak havoc if they contaminate the clay, and they dry too fast, till they contain too much water, then they dry too slow, which leads to frustrating inconsistent....
I use and fully recommend ONLY HardiBacker 1/2 "cement" board.
Don't know if it's available in the UK, but I swear to God I'd pay to have it shipped in, it's that valuable.
Grogged stoneware can be rolled out instantly, porcelain takes a bit longer, but this time also allows the more compression ribbing porcelain appreciates to remain straight.
6-12 strokes straight down, 1/4 turn, repeat till all 4 directions complete, flip, repeat the process.
Grogged stoneware is ready when both sides are complete.
Porcelain after both sides are done twice.
Side note...
It takes some practice, but I've found that holding the (wooden) rib at different angles is also better for each.
Stoneware, /
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Porcelain,
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Sorce