If by “proficient” you just mean “knowing how to do it”, then you could learn HTML in that (short) timeframe, I’m sure.
However, to be good at it, is an entirely different story, and will take lots of practice and experience.
HTML as a language is fairly easy. It won’t take all too much time to learn the basic foundation of it. But then you need to learn how to apply it properly, and that could take a lot of time.