I've been reading Spengler's Decline of the West, or trying to at least. I think I'm around to chapter 5.
On the subject of time and space, I think it is very important to understand that Spengler is coming from the German Idealist view of the world, which is about as radically different from the English view of the world as you can get. In the English view of the world, which is the way of viewing the world that all of us here probably have, the human organism is an animal that exists in a material body that exists in time and space. Stars, chairs, animals, rocks, and planets, and so forth, are all every bit as real as you and I. In fact, in a way, they can be more real, because stars and planets are supposed to have existed long before humans existed and will exist long after. In fact, under English evolutionary theory and cosmic models, the universe is supposed to have existed long before humanity. Further, the information that science provides about this world of stars, planets, and animals, is supposed to be at least somewhat accurate. When we see an object, the way that object exists in the universe is supposed to be similar to the way we see it. And when we think about things rationally, we suppose our thinking to correspond, more or less, to the way things actually are. The universe abides common principles which we call Nature, and science is able to understand nature. In short, humans are not the center of the universe, and human senses, reason, and science are competent to try to undertsand the vast universe.
But in Prussia, along came Kant. Kant argued that actually human sense organs add something to the experience of objects that is not there in the world outside of our minds. English philosophers like Locke had already claimed that things like color are parts of experience that your mind or sense organs add, but that other parts of experiencing an object, like the dimension and width of an object, really are there. Kant went much further than Locke, and argued that basically everything we experience about objects is added by either the senses or the way the mind structures and interprets experience. Kant argued that time and space were not parts of objective reality, but actually are purely subjective, and a part of how the mind structures experience. They do not, according to Kant, exist in reality. Causality, likewise, is added by the mind to experience, but is not a part of reality.
Then came Hegel. Hegel took Kant's theories even further. Kant still believed in some kind of reality beyond the human mind, because he believed that this reality was necessary to provide sensory input. Hegel did away with this altogether. The only thing that exists, to him, is mind and experience. Further, Kant understood that while it was the mind that shaped experience, it was always the mind of the individual
human being. Hegel did not share this belief. He thought of mind and reason as being collective, and belonging to nations and cultures. This idea sort of makes sense when you think about language, which is necessary for reason (probably), and which belongs to and is created by cultures. Hegel also believed that only the whole is real, and parts do not exist absent the whole. This means that Hegel believed that only cultures exist. Stars, planets, animals, and individual human beings are creations of the reason and mind of cultures. Almost everyone who came after Hegel disagreed with him in some significant regard, yet they all agreed with Hegel and Kant on reason's incompetence to understand any sort of reality outside of the mind.
I think that understanding the above is necessary to understand at least some of what Spengler says, because otherwise his claims seem kind of weird.