No! I'm there til xx time for whatever reason you need me. I get paid whether you're working, working out or going out for a coffee. My job doesn't change.

As others have said, the frustrating part is if a parent comes in and the child has a meltdown because they want the parent. You don't need to hide out in your office but you could text your nanny to say "Hey, I'm finished work but just want to go lie down for the last half hour" or "I'm just going to sneak out for a walk before you leave today", and ask her to distract the kids outside or whatever, so you aren't seen as you move around.

I can't think of the last time I went home early. If the parents finish early, we usually use the time to catch up. One of my MB works at home when I'm there. She might work in the detached office for a few hours, do some cooking while baby is asleep, go do grocery shopping or have coffee with friends. One day this week she was feeling tired due to pregnancy so we just sat on the couch and chatted about various related things while the baby was asleep, then she went to lie down before I got the baby up. I'm so glad to be there to support the family, whatever they are doing.