On the practical side, the M’nos HaLevi writes that one reason for Achashverosh to wait twelve months to have relations with the young women he had collected was to make sure first that they had no STDs or other illnesses. He needed twelve months for this, writes the Malbim, because there are some health conditions that are only apparent in certain seasons. After twelve months, they could be observed in all four seasons, and would thus be checked out and ready for the king.
Although we rightfully think of Achashverosh as an evil man, the Maharal notes that this verse demonstrates his self-control. Even a wicked man can have positive attributes. That, writes Maharal, is a kind of tznius, which is usually defined as modesty. Tznius is really a form of discipline, or self-control. In “A Canopy of Brocha,” a series of recorded lectures in which Rav Avraham Chaim Feuer discusses the Halacha of married women covering their hair, he points out that Hebrew word for “hair” (“se’ar”) is the same word as “storm.” In other words, reigning in and controlling hair is the real reason for covering it. This tznius, according to the Maharal, is the reason Achashverosh loved Esther (see 2:15 below). People love in another what they see in themselves. Even regarding the idea of “opposites attract,” the two parties involved like each other because they compliment each other.
Mystically, Rav Shneur Zalman of Liadi notes that these twelve months can be divided in two: one half for myrrh, and the other for spices. That being the case, he writes that the first half represent the half of our time on this world that we use meditating on the bitterness (“mar” means “bitter” in Hebrew) of life, and the other on the feeling of G-dliness (“bisamim” represent uplifting spices). It is indeed a constant battle to reach a middle ground between these two extremes. Our souls yearn for the spiritual world while our bodies are contented with the physical.
The Vilna Gaon proposes that this verse alludes to the idea that many things are allowed for a half and forbidden for a half a year, like intimate relations.
The Rema reads this verse as a reference to the fate of wicked people in Gehinom. There, the first six months are a time of extreme suffering, and the last six months are a time of easing up of that pain.