Unfortunately in the white collar world.

it was instead of my regular work,

'regular work' typically isn't covered by someone else.

It piles up until you get to it.

labor laws are tricky, but in general they need to assign you an amount of work that can be done in a reasonable amount of time

I very much doubt it. It may help your argument when you're applying for unemployment but I very much doubt it's illegal for them to assign whatever work they feel like reasonable or not. Unfortunately.

I was literally told once “yes we can have meetings all day because you have all night to finish your code.” The same was expected when they had ‘team building’ outings.