How long did it take for classical music to be written in the 18th century?
It took 24 hours for classical music to be written.
Wow! I did not think it took such a short time.  Was this in consecutive hours of work? Or work done in a linear time path?
Isn't it incredible! They had a twenty-four hour rule, in the opera and theatre community. The twenty-four hours were filled with celebration revolving around the music.
How did they get the work done if they were celebrating?
The people would surround the 18th century artists, while they were creating to listen and give input, while also enjoying the music.
Very interesting, I would imagine there would be drinks involved as liquor was common during the 18th century.
Yes, however Parliament passed the Gin Control Act of 1729 which raised the taxes on alcoholic beverages! So, the composers would definitely limit themselves.
Thats very funny.  I believe they would also indulge in other party favors as well. 
I would imagine they ate quite a bit of cheese, bread and proteins!
Interesting.  Do you know of any classical musicians that enjoyed any more extreme party favors? 
I believe that many of them endeavored in more extreme favors. For example, Berlioz was known for taking opium and Stravinsky was often heard of taking behavior modification drugs.