Questions & Answers about Гость планировал визит на два дня.
Why do we use на два дня here instead of just saying два дня?
When you talk about the intended or planned duration of an event (like a visit or a trip), you use на + Accusative. If you dropped на and just said планировал визит два дня, it would mean the actual process of sitting down and planning took two entire days!
Since на takes the Accusative case here, why is the word for day written as дня (Genitive)?
The preposition на affects the whole phrase, but it directly hits the number first. The Accusative form of the number two for inanimate nouns is два. Then, the number два follows its own rule: it requires the noun after it to be in the Genitive singular. So на controls два, and два controls дня.
Why does the word визит not change its ending if it is the direct object being planned?
It actually is in the Accusative case because it is the direct object. However, визит is a masculine inanimate noun. In Russian, the Accusative form of masculine inanimate nouns is identical to their Nominative (dictionary) form.
Could I use the perfective verb запланировал instead of планировал in this sentence?
Yes, you could. Using the imperfective планировал focuses on his intention at the time (he was planning). The perfective запланировал would focus on the completed result of making the plan. Both are correct depending on what you want to emphasize.