Hey, it certainly sounds tempting, but has several issues. I have just come to the end of my PPL, test next week and has taken 18 months due to money, time and weather in the UK.
But, in 21 days, i can't imagin it being easy to do all of the theory and practical in 21 days. In the UK we have 7 written and 1 oral exam, but in the US, i believe its 1.