You create a shadowy door on a flat solid surface that you can see within range. The door is large enough to allow Medium creatures to pass through unhindered. When opened, the door leads to a 30ft by 30ft by 200ft plane filled  with wildlife that takes form through your imagination. When the spell ends, the door disappears, and any creatures or objects inside the demiplane remain trapped there, as the door also disappears from the other side.

Each time you cast this spell, the perimeter of the spell is doubled, so the previous Wild-plane is now quadrupled in size, adding more imaginative and colorful interpretations of the magical forest, plain, tundra, reef, cave, riverbed, jungle, or other biome you wish it to be. By the time it's 120 by 120, wildlife starts appearing. By 1920 ft by 1920 ft, you start to see an ecosystem developing. Each time the door closes, you lose access to it and the plane waits for you. In this stage, the plane is accessible to anyone casting the Demiplane spell who knows well the nature and contents of your plane.

At higher levels. Once this plane becomes 1920 ft by 1920 ft in size, the work of roughly 8 days, you can choose to anchor this plane to reality, becoming, in essentially, the Archfey of your own demi-realm, by casting this at 9th level. You must cast this spell on a fully material plane, such as the Prime Material Plane or the Feywild, or an inner plane such as the Elemental plane of Wind. The plane warps reality at the point of casting, forcing a door into existence in between the threads of reality. You also choose a different plane not controlled specifically by any deity that is not another demiplane, and your Wildplane becomes a mix of that and the plane you cast the spell on. This second plane must be intimately familiar to the caster, such as a place where the caster lived for several years, or a place from which their patron or divine benefactor hails. The sky seems to appear as a child of the two plane's skies (yes, there is a sky now, and less of an apparent height limit) and planar sense would give a plane shifter a sense of closeness to both planes. The plane is constant even after the caster who owns it dies, upon which it becomes uncontrollable and much more unstable, and must be destroyed via magical means of ninth level magic, divine magic, or the power of great artifacts like the Deck of Many Things. When the caster creates the plane, they can choose how it bends time:

Stretches time: One hour in this plane becomes a Day in the Prime Material Plane OR The plane upon which the spell was cast.

Shrinks time: One Day in this plane becomes a Day in the Prime Material Plane or casting plane. 

The owner and all who they permit can plane shift off of this plane to one of the two source planes at will, ONCE they visit the edges of the plane, which is in a 10 mile radius sphere with a sky and a ground 2 miles deep. 

The caster can expend a ninth-level spell to repair any damage or drastic changes to their plane while in it, and their spells which change the environment of an area can be used to change various spaces or entire sections of the plane with the casting of a spell. The spells Control Weather, Earthquake, Storm of Vengeance, and Sunburst are all Lair Actions for the caster when in the center of the plane. They can cast any fifth level spell relating to elemental effects (not damage) or wind and water at will, as long as they do not affect a creature negatively directly. They can cast Travel By Plants at will in their plane. As for the time alteration, rests do not take less or more time. The caster has no difficult train in their own plane, although they can make the terrain difficult for others