after normal working or opening hours, typically those of bars and nightclubs [as ]
she was going in to work after hours
: to work at odd jobs especially those requiring little training or skill
gone in to work in town, odd-jobbing — Paul Annixter
Tell me please what go in to work means. Why not go to work ?
There's not much difference. Somebody who works in the same building every day might say either.
A self-employed plumber with no regular place of employment would say 'I'm going to work'.