There is no simple answer to this question as it was presented. There are various strategies from time to Level based to start injection. But consensus is generally to keep it going after switch until the steam to blowdown has started.
There is always some fines entrainment to the fractionator at the end of filling. Managing over time is the key to long term reliability. But if entrainment for 1 cycle is higher than normal, yes additional AF injection would be a good idea.