Wow, learning the clock in yur dream is an awesome experience. But I would guess, that it didn't come to you just out of the blue. You probably heard an explanation of the clock before, maybe someone tried to teach you, or you had some other info already in your mind from your normal daily activities, even if you didn't really pay attention to this info, you still saw it and it was stored in your mind. And in your dream, your mind just organized it for you and you had a moment of sudden realization. This doesn' make it any less cool, and of course, I could be wrong.

It happend to me maybe once, when I had a problem, had all the info available, but just couldn't figure out a way of proceeding. Went to bed with this on my mind and when I woke up, my first thught was "I got it!". I have somehow figured it out in my sleep.

I would say, that you can't really learn something totally new in your dream (LD), if you have no information about that what so ever. For example, I don't think I could learn japanese in my LD, since I have never studied that language, never read the dictionary or any text books.

But you can practice and get better at things you already know or just learning. I have read that some athletes practice their sport in LD, a surgeon practiced his surgery moves, a molecule of benzen was 'invented' in LD, a periodic table of elements came to Meneleyev in a dream, and so on.

There definitelly is a potential. Who knows, maybe in the future, when everybody is LDing, that's how we'll practice and learn.