overtime rates?

[stella1w]

I will be employing a nanny for a 50 hour week. How should I work out an overtime rate in case I am held up at work - or even have a pre-organised night out every few weeks or so?

IME it's normal to have a pre-arranged babysitting rate, usually not higher than typical hourly pay, and an unscheduled overtime rate, which may be a bit higher to reflect the inconvenience. Different areas have different customs though.