When did the two kingdoms of Egypt merge to become one?

It’s difficult to pinpoint an exact date for an event that took place so long ago, but we know that the Upper and Lower Kingdoms of Egypt were united sometime between 3150 BCE and 2680 BCE.
It’s generally accepted that King Menes (also known as Narmer) of Upper Egypt was responsible for the unification. The Narmer Palette, which shows his victory over Lower Egypt, has been dated to around 3000 BCE, near the beginning of the First Dynasty. The Palette depicts Menes/Narmer wearing royal crowns in the style of both regions, indicating his rulership over the entire land.
There are two important symbols in Egyptian art which represent the unification of the two kingdoms. The first is the Pschent, a double-crown. (In the attached image the red part shows the crown of Upper Egypt, and the white part of Lower Egypt.) The second is the sema tawy, which shows reeds and papyrus plants being bound together. These images don’t appear in Egyptian art before the unification, so archaeologists use them to help date the art pieces as well as to support their own theories about when the unification actually took place.
https://www.ancient.eu/Narmer_Palette/