That would depend on how much the chain has worn before it was replaced.
By replacing chains often, or keeping spares to use in rotation, you can make sprockets last much longer.
If you let the chain get worn out before replacing it, the sprocket will not work well with a new chain and the new chain will wear out very quickly.
Replace the sprocket when it doesn't seem to mesh perfectly with your new chain. Or
If you have just bought a new chain to replace a worn out one but you don't have the sprocket yet, then just keep using the worn chain.
10 full links of new chain measures 254mm
Replace the chain when it stretches (wears) to 255.5mm
Replace the chain and sprockets if you've let it stretch to 257mm (so keep using the worn out stuff, either until the new chain and sprockets arrive or until they stop working at all)