If I was consistently working late due to this reason, my employer would have a problem as working late is not in the company culture.

I can understand someone doing this out of personal preference, but is working late considered the norm and is expected by the employer?

Company norms and cultures aside, the software industry was built on working late. Whether or not the CEO goes home at 5pm, the software part of a software business needs to get built, and it's usually not done 9-5.

It obviously depends on your employer, but it's very common for managers to write off people who go home on time as not the right kind of material for promotions, etc.