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Normally a cell has a mechanism that controls its division. As far as I know, it checks surface area and stuff like that to decide to go for mitosis or not.

However, this is not the case for a zygote. A zygote, after around ~14 days starts to divide rapidly and forms the blastula. What mechanism controlls this "rapid division"? Why can zygote divide rapidly when it has not reached a high surface area or doesn't have enough mitogens to induce the cell division? Does the zygotes mini-cells have a cell cycle like other cells but they are really fast? Or do they just copy the DNA and divide rightaway?

And when I first saw the video of this stage, I was surprised. The DNA is a one long molecule; how fast do those replicators work?

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A zygote generally has a lot of nutrients, essential biomolecules like RNA and proteins and cytoplasmic organelles for rapid division. So the cell does not grow and divide but rather undergoes "cleavage" (there is no G1 phase of cell cycle). However, it still undergoes DNA replication. And yes, DNA replication is fast because it is initiated at once from several parts (origins of replication) of the long DNA (it still takes a few hours† ).

† See:

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