I'd say that XML could be mastered within a week, if you understood the underlying concepts and if "XML" just meant the markup language and nothing else.
But the only drawback here is that you will have to live on the mercy of others by asking them to help you. I was looking for some self study / self learning kind of stuff to get me going.
There are lots and lots of design patterns of different classification. You've got creational patterns, behavioral patterns, structural patterns etc. Some are documented, some are not (and in turn may not be recognized).
"For the last 5 years I have been running a mobile/telecom space consultancy startup. [...] Last month I decided to call it a day."
If I mention something like “Project Manager” then at some point in time, especially when they conduct background checks, I will have to come out with the truth which again will put me in a difficult situation.
I have a idea for a web-based startup that I think would provide major time and cost savings to my field, as well as several other verticals.