If your workplace is suffering from a long hours culture then it should be perfectly possible to work shorter hours and still get your work down.
The first step is to work out where your long hours culture came from. If it has just gradually crept up on you, then perhaps you need to agree with your colleagues to just say no.
Start with Work Your Proper Hours Day, and keep it up. Make sure you leave at a reasonable time each day. Keep a rough diary of peoples’ hours.
If people are staying on late, because that’s the way to get on with the boss, then you should plan together with colleagues to beat the vicious cycle. If there are brownie points for being the last person in the office, then all leave at the same time. If people who skip lunch, curry favour – then all go out for lunch together. Start doing it once a week. Ask the boss too!
You should try and raise it with your boss too (this is much easier if you have a union rep to do it with you). It’s not efficient management to judge people by their hours. You should be judged by your performance, not your presence. If they say there needs to be someone in the office late, then suggest you could work out a rota.
And you may need to be clear that the opposite of a long hours culture is not a clock watching culture. In many jobs there may be a need to work harder and for longer hours every so often. There may be emergencies. Be clear that this is not your problem, it’s hanging around when there is no need to, or just in case, that is the issue.