Nov 4

On November 4, 1783), Mozart's Symphony No. 36 "Linz" premiered. He wrote to his father on October 31st,

"We arrived here safely yesterday morning at nine o’clock ... On Tuesday, November 4th, I am giving a concert in the theatre here and, as I have not a single symphony with me, I am writing a new one at break-neck speed, which must be finished by that time..."

https://theblueblot.wordpress.com/2012/08/27/the-simplicity-of-kindness-hospitality-and-good-claret-mozarts-36th-symphony/…

It means he finished this symphony in a few days.