Am I being unreasonable?

I think it depends on what time your daughter goes to bed. Will he still spend time with her when he comes back from gym? Or weekend?
And do you have some time for yourself regularly?

You're not unreasonable then. He sounds a bit selfish. He should do more for you and your child.

I think it’s absolutely fair and reasonable for him to suggest 6pm to your neighbour. It’s only half an hour later but makes a big difference to your family! … I bet he’s not even suggested it 👀

It's nice for him to have a friend and an activity but this is just ridiculous. I would sit down with him when your daughter is in bed, not when he's going out of the door, and explain that you're happy he's going to the gym but there needs to be a compromise because he's losing time with his daughter and it's going to have an impact on their relationship. I'd possibly lead by asking if he's OK, because losing the only 30mins you spend with your child every single day makes it seem like he actually is trying to avoid her. Is he depressed? Talk about compromise - could he go two days a week? I'd also casually mention the time if you see the neighbour in question like "would be nice if it was 30 mins later lol", I bet your partner hasn't even thought to suggest changing the time, or didn't want to suggest it. Is there also potential for a compromise to be made on bedtime? Idk how old but those are brutal working hours and there's probably not much bonding time pre bed anyway- is he present on days off?

He should go before work

I totally get this. It annoys me when my partner finishes work, gets home at 6:30pm and then *has* to decompress in the bedroom by himself as soon as he gets in rather than hang out with his daughter. I understand that he’s tired, but she goes to bed at 7 and I do all of the bedtime routines so why not just push through and then relax properly for the night?!