I think 1% to even 0.5% is pretty likely - at which price maybe you might have to accept something maybe 15-20% below market. I would love to see early developers at this stage get 2-5%, though I think that would be hard for some to push all the way through (past the CEO if applicable, board who has to sign off on the cap table and doesn't want the option pool to be too low too soon, etc).
But would it be fair if you are good and putting in that much work? Hell yes. But likely you're good, and hopefully the work/life balance isn't that lopsided either. Are you going to get it? Unlikely.
I joined Milo.com about a month after the A round was closed, everyone post-A was given between 0.1 and 0.3%. If you are joining early seed round, you would probably expect around 30k in salary and between 1% and 5%. The question is how much do they want you to join, and can you sell yourself a little bit. Find out what their pain points are that you think you can honestly attack on day #1 of joining, and make sure they know you intend to fix those problems ASAP. Then tell them what you think is fair, and let them agree to that (or don't join). As an engineer you shouldn't try to negotiate too much with a founder because: If they are bad at negotiating, the startup is going to fail, and if they are good at negotiating they are going to convince you to take a really bad deal (and you will be happy about it).
If you are an engineer that is good negotiating, you shouldn't be joining someone else's startup (you should be working on your startup, even if you are 15).
In my example I'm talking about a seed stage startup where the engineer being hired is going to be a critical part of the team and has relevant experience. No board, no major dilution yet. Don't get me wrong, 2% is much more applicable than 5%, but I don't think 5% would be unheard of.
A month ago I talked with a founder of a company with a huge angel round in the bank looking for an experienced technical lead, and he was very comfortable giving ~2-3% equity for it (smart guy!).
Perhaps 0.5%-1% is more common, but that doesn't mean you should take the job at that level. I was answering the question of what this type of hire is worth, not what they commonly get.
But would it be fair if you are good and putting in that much work? Hell yes. But likely you're good, and hopefully the work/life balance isn't that lopsided either. Are you going to get it? Unlikely.