I don't know as it matters, really. Just choose the departure time from Rome that suits you best. We're early risers, and would personally wish to get the journey over with earlier rather than later to have more versus less of the day to enjoy at our final destination. That said, night owls might need more ZZZZZ time in the morning.
Editing to add: I haven't done this myself but if you haven't purchased tickets yet, you might explore high-speed rail (Trenitalia or Italo) to Salerno, and then ferry to Praiano. There didn't used to be any ferry services to that village but it looks like Travelmar has 4 or so seasonal runs now from the Concordia port in Salerno...which is walking distance from Salerno Centrale station.
Input your date of travel and see what comes up? We're all different but if at ALL possible, I'd personally opt for ferry over road travel in the AC any day.
https://www.travelmar.it/en/index