Three hours is enough for a satisfying, if selective, visit — the trick is committing to skipping sections in advance rather than deciding on the fly, which tends to eat time without adding much.

A guided tour is especially useful at this length, since a guide's fixed, efficient route removes any risk of wasted time or getting turned around.

If a choice has to be made, the Sistine Chapel is worth prioritising over the Basilica in this window — it's the reason most visitors are here, while the Basilica, being free and independently accessible, is easier to return to on a later trip.