What is the primary reason a close approach involving Mercury or Venus requires checking local rise/set times relative to sunset or sunrise?

Answer

They are inner planets whose visibility is governed by their proximity to the Sun.

Mercury and Venus orbit closest to the Sun, meaning their visibility windows—short periods near dawn or dusk—are dictated by the precise timing of local sunrise or sunset relative to their position.

What is the primary reason a close approach involving Mercury or Venus requires checking local rise/set times relative to sunset or sunrise?
astronomystarplanetMoontonight