Am I charging correctly for Overnight bookings?

First, have you established a House Sitting fee? That would be the first thing. You could charge a day of House Sitting plus an extra fee for the added hours.

Hopefully someone else will chime in with more wisdom, but beyond that, here's my two cents:

A dog being boarded overnight will spend at least 7 of those hours sleeping, while you are also (hopefully) sleeping. That makes $25 night a fair price (for you).

During the day, you could be out doing more walks and check-ins, in addition to other necessary and/or fun activities. Therefore, your daytime hours are much more valuable. How much are your daytime hours worth to you? What do you want to make per hour? If you are expected to stay with the dog every moment for 9 hours, you should multiply that hourly rate x 9.

I hope that starts a conversation for everyone!

Best of luck!