I usually go for first appointment of the day or thereabouts. 9am-10AM if possible. Idea being they’re fresh and haven’t been worn down by seeing a lot of people already.

I never make appointments for the later afternoon. Last thing you want is someone that’s tired and trying to hurry up and get home. Also avoid Friday afternoons. I’ve heard stories that manufactured things that have serial numbers that say they were built on a Friday afternoon have a far higher warranty claim rate.