Yes, there are likely people who have. There are many determined writers out there who thrive under time constraints. They might have a clear plan from the start, know their characters well, and be able to write steadily each day to reach the goal.
Yes, it is possible. Many writers have successfully completed a novel within 30 days following the concepts in '30 days to write a novel'. It's all about discipline, having a basic plan, and sticking to a daily writing routine. You don't need to write a perfect draft in one go. Just get the words on the page and worry about editing later.
In 90 days to the novel, one could complete the first draft. This involves coming up with the story idea, creating the main characters, and outlining the plot.
Yes, I'm sure there are many. There are writers who thrive on structured programs like this. They find the discipline of having a set number of days to complete a task very motivating.
In 47 days to change fanfiction, one could focus on improving the plot. Maybe add more complex storylines, unexpected twists, and turns to make it more engaging for readers.
No, it's not a common expression. Most often, we hear about general time frames like a year or six months to write a novel, but 738 days is rather specific and not typically used widely.
One challenge is time management. You need to be strict with yourself and allocate enough time each day for writing. Another is avoiding writer's block. It can be difficult to keep the story flowing continuously for 90 days. Also, maintaining the quality throughout the novel can be tough as you might be rushing to meet the deadline.