"If I leave at five, it'll all fall apart"

Behind a lot of long hours is the feeling that you're holding the place together. You're the one who knows how the rota works and spots the problem before it lands. People come to you when the system does something strange. If you weren't there in the evenings, catching things, you feel they'd start to slip.

Some of this is true, and you should take the credit for it. You are good at your job, and things do go better when you're paying attention. But the belief has three weak points.

The first is the evidence of your own absences. You've been on holiday, and you were off for a week with flu in February. The department didn't collapse. Some things waited, other people dealt with a few of them, and one or two were done differently from how you'd have done them and turned out fine. You came back to a full inbox, certainly. But nothing had fallen apart. If the place can survive your being in Portugal for two weeks, it can survive your being at a swimming gala on a Thursday evening.

The second is that your availability shapes how other people behave. If you're always there and always answer, your team learns to bring things to you when they could resolve them themselves. They do it because it's quicker and safer than deciding for themselves, and it doesn't mean they're incapable. Each time you catch a problem at seven in the evening, you take away a chance for someone else to learn to catch it. After a few years of this you really are indispensable, because nobody else has had the practice. The long hours helped create the dependence that now seems to justify them.

The third is what indispensability is worth to you. It feels like security. But someone who can't be spared from their present job can't easily be promoted out of it, and an organisation that depends on one person's unpaid evenings is fragile, and a good manager above you would see it that way. A team that carries on working when you're not there reflects much better on you.

There's a fear underneath this that deserves saying out loud, and I'm offering it as a possibility. If you left at half past five and nothing went wrong, that would prove the evenings weren't necessary. Part of you may not want to find that out. The hours have been a large part of how you see yourself, and it's uncomfortable to learn that they weren't holding anything up. I'd say it's much better news than the alternative. It would mean your value to the place lies in your judgement and your skill, which you'd take home with you at half past five and bring back in the morning.

You can test this one. Pick one thing you currently keep hold of because nobody else does it right, and hand it to someone on your team, properly, with the authority to decide. Expect it to be done differently from how you'd do it. See what happens over a month.