Write out the baby's schedule so the nanny can keep them on it. Make sure you tell the nanny to help themselves to drinks, food, which bathroom to use.

Absolutely. Check your baby monitor/cameras if you have them and want to see what is happening.

Any advice for first time parents doing their first trial day with a nanny candidate? Baby is four months old. Is it okay if we are around for part of the time and then leave nanny with the baby for the rest of the time?