Not everyone has the ability or personality to be a hyperfocused genius working on a difficult task. Even if they could, it's simply doubtful that a learner would pick up everything necessary to be at C1 level in 5 months. On Chinese-Forums we have a few posters who have done intensive full-time study of Chinese using modern methods for months, and I don't believe any of them managed to achieve that level in several months. A2, B1, yes.

See this long debate about whether a guy can achieve C1 fluency in 3 months:

http://www.chinese-forums.com/index.php?/topic/36222-benny-l...

The proof is in the pudding - pass a C1 test after 5 months, starting from 0, and we'll all acknowledge it's been achieved.