Why can you do it? Well simply, because you do it, you pay attention to it. It’s not that surprising.

When you’ll open yourself to that kind of capacity that you may have, you’ll see more and more weird strange time-related phenomenons, the so called “coincidences”, that may or may not be explained one day.

Just be careful about all the “all-knowing” brainy educated people, who will tell you that you hallucinate. You don’t! When you’re sick of it (of them), just ask them “what causes placebo effect”, and enjoy watching them totally drying up… ;-)

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[Edit][for the all-knowing brainy educated people] The brain is composed by 10^11 (=100 billions) neurones, and has maybe as many features than that. No one can “science” that level of complexity, therefore we do knowledge on the brain the other way around: we look at what it produces, and then we assume that it's what it does.

Ergo my answer: “you can do this… because you do it", just like you do absolutely everything else. Why aren't you surprised by the everything else that you do, and focus on that tiny little feature of knowing the time? Of course you know the time, isn't that a simple feature? It looks like simple to me.

We can't predict what the brain can do because it's way out of the computability spectrum. So unless we have an infinite computing power, we will never be able to tell that. The brain is the knowledge machine, but fire can't burn itself, water can't wet itself, a knife can't cut itself… therefore you can't “know your brain”, so it has to be a mystery to yourself, and questioning it is irrelevant.