Learn Croatian: Planiramo lansiranje sredinom studenog. - We are planning the launch in the middle of November.

Sredinom is the instrumental case of the noun sredina (middle). In Croatian, this specific instrumental form is used as a temporal preposition to mean 'in the middle of'. Whenever you use početkom (at the beginning of), sredinom (in the middle of), or krajem (at the end of), the timeframe that follows must be in the genitive case. That is why we see the genitive form studenog here.

Why does the word for November look like an adjective (studenog) instead of a regular noun?

Unlike most months in Croatian which are regular nouns, studeni (November) is technically an adjective meaning 'freezing' or 'cold'. Because it is an adjective, it declines like one. In the genitive case required by sredinom, it becomes studenog (or sometimes studenoga), using the standard adjective ending for masculine words.

Could I say u sredini studenog instead of sredinom studenog?

Grammatically, u sredini is possible, but native speakers rarely use it for time. U sredini is generally reserved for physical space, like u sredini sobe (in the middle of the room). For points in time, the instrumental forms početkom, sredinom, and krajem are standard and sound much more natural.

Does lansiranje only refer to rockets, or can it be used for products and projects too?