What is the position regarding the zakat on real estate that was intended for investment/saving, and was received after a period of time, and is it considered among trade goods, and when does the calculation of its zakat begin?

If you are not firm in your intention to sell the apartment, there is no zakat due on it, because it is not considered a trade commodity. Hesitation in intention does not make it commercial. This is based on the Prophet's (peace be upon him) saying: "There is no sadaqa (zakat) on a man's slave or horse." Similarly, Sheikh Ibn Uthaymeen (may Allah have mercy on him) said: "There is no zakat on this land to begin with, as long as he does not have a firm intention for it to be a trade commodity. So there is no zakat on it because he is hesitant." However, if you firmly intend it for trade, zakat becomes obligatory on it according to some scholars, while the majority view is that it does not become a trade commodity unless it was intended for trade at the time of its acquisition.