When I got the current job I started to work on an Android app that a coworker which left the company was doing.
The app was ready at about 40% and was barely usable, it lacked a lot of features and multithreading so with a huge amount of data it used to crash (Android doesn't allow you to make the app freeze for more than 2-3 seconds, it considers that the app is not responding anymore).
After a week or two the work to do was still huge, but one day one of my coworkers came in and ask me if I was able to release a beta for a client the same day... Unexpected deadline.
I spent 8 hour fixing as many bugs as possible and adding multithreading in the most weak parts.
I did it but it was so stressful and the result wasn't even great. In fact I finished the stable version 7 months later.