As Russell says the spalting stops when the wood dries out indoors.
You will need to treat the ends of the long grain on each piece with melted paraffin wax, end seal, pva or gloss paint or similar straight away to minimise end splits which will appear very rapidly otherwise as the timber dries out.
Likewise if you have any pieces with the central pith in, consider splitting or sawing them through the pith as this is where most end splits start from.
You will still end up with some amount of firewood even after doing this but if you do it straight away you should hopefully still have some good and useful blanks for your turning.
Cheers, Paul