On our last tour, Best of Switzerland our flights were from Detroit and we live 2 hours west. We did a park and stay that cost about $25. more than just parking for 15 days. Booked with hotel directly and had hotel room after our return to the states. Despite a “daytime” flight home, we were up 22 hours by the time we landed in Detroit. It was great being able to crash, sleep in and drive the 2 hours home rested.
We arrived 2 days early and explored things in Lucerne not on the tour, and added one day at end. We stayed at the Blue hotel at the hotel in Zurich, not a central hotel that we like, but darn convenient to flying out the next day.
2 years ago we arrived one day early for Heart of Italy. Visited the Borghese the day we arrived and explored some on our own the next day before the tour. After tour ended we took train from Florence and stayed 3 nights in Venice.
Your flights are a huge expense, so if time allows adding on both ends of the trip is worth it. I wouldn’t do a tour without arriving at least one day early.