One month
Suffice to say, Lex's first month in the academy was extremely busy. Between his various classes, doing his own research for the impending field test, and cultivating when able, he barely had any free time.
That limited free time that he had was often spent in the company of Amelia and a few of her friends. Truth be told, she was as helpful, if not more, in bridging the gap between Lex's knowledge and common sense in the Crystal realm than many of his classes.
For example, the device that looked like a watch he was wearing today was called PT (personal terminal) which, for all intents and purposes, was like a mobile phone but with more features, given to him by Amelia. He was also better able to get accustomed to the day/night cycle here, as well as understand how the calendar in the crystal realm worked.