We do pay our helper "overtime" for working after 8pm, although it is not the norm in HK. We started doing this years ago when we hired her as it seemed more normal to us (from the US). Pretty sure we would do this again if we hired another helper. However, we don't think that our helper has come to expect it, even six years on she is very appreciative. I also think it makes her feel valued as a hard worker, although there are other ways to do this, giving her a bit extra for "extra" work is an easy way for us.