The convention below should set the default precision for all datetime objects in the model to 6 but currently it is a NOP. The other overload is .HasPrecision(byte, byte) and using this instead has the same behavior.
Convention:
modelBuilder.Properties<DateTime>()
.Configure(c => c
.HasPrecision(6));
Convention:
modelBuilder.Properties<DateTime>()
.Configure(c => c
.HasPrecision(6));