I have a few friends like this, although usually its lateness rather than being too early. I was frequently finding myself in situations were people would seemingly just ignore my schedule and expect an arrangement to wait and begin on their time alone.

Best way I've found to combat it is to give windows rather than start times and make arrangments that you can enjoy on your own if they dont turn up. "I'll be online between 6pm and 7pm", rather than "I'll be online at 6". That way, the fact that we only gamed for 15 minutes is entirely on them when they're 45 minutes late.

I've also starting forcing people to be specific by turning down arrangements that aren't. "I can probably get to the pub around 8 depending on work" is now met with "Alright mate, let's arrange something for another day if you're not sure". Again, it puts the onus on them rather than having a fallback of "I said AROUND 8" at 9:15.