[fian]

Uninterrupted time is definitely a factor.

The other factor is when you are supporting a deployed application, you will receive bug reports that require "urgent" attention so end up working late to identify it and either resolve it or detail a workaround until a permanent solution can be found.

Also there is an expectation that IT people will keep up with advances in technology, so many of us spend time at night researching and testing stuff out to keep abreast.