Does it look bad if I email an employer before getting an interview about working hours?

Wait until you're talking to a human, at least.

Not "we've received you're application and we'll get back to you" (even if that appears to have been written by a human specifically to you), but rather "we're interested, let's talk".

Before then, you're most probably still in a pool with a really large number of other candidates.

They will try to draw a conclusion about you using any bit of information they have available, which most definitely includes the questions you ask.

I might even suggest waiting until much later if it's more just idle curiosity than something that will actually affect whether or not you'll take the job (because there always at least some risk of being judged for asking this question too early).

This is not the type of question likely to make a good impression.

There are some really good questions one can ask, that could fast-track you to an interview, although these are typically about showing interest and excitement about what you'll be doing or the company, or (subtly) demonstrating your knowledge about the domain.

All this question tells them is that you care about the hours you work, which most people do. Although asking it too early might tell them you care about your working hours more than most, which may indicate future issues about your interest in the job, performance or flexibility when it comes to working hours.

Some companies offer flexible working hours, but that's common enough these days (at least in some industries) that you asking shouldn't really make them think you'd be a good match. If this is what you're looking for, specifically asking whether they have flexible working hours would be better here, but only marginally, and it would significantly count against you with companies that don't (which you may consider acceptable if you'd never accept a job at such a company).

This is not to say it's likely to make a bad impression, but there's a risk of that, and there isn't really any real upside for you to ask this question before you've actually gotten their attention.