I never related to "time blindness" because I was always consistently early for things, but really I was just deeply anxious about being on time for things. I would set like 10 alarms set, I wouldn't be able to do anything for an hour or two beforehand because I was worried about being late, and I'd usually show up way too early because I couldn't actually estimate when I needed to start getting ready to be on time. That doesn't exactly sound like the behavior of someone with a functional inner clock.
I too got (re)diagnosed in my 30s and prescribed Concerta. Rediagnosed because my mom then told me I'd been diagnosed as a child and she just never told me. Finding the right dose took some trial and error, and to be honest "the right dose" is something that will probably vary throughout my life based on how good my non-medication ADHD management is going. But for me it's been life-changing without burning me out, and it's been almost 7 years.
I also think even without the medication the diagnosis is worth it. It clarifies your life somewhat, if there are things you have struggled with that it explains.
Yeah, I think our society views so many symptoms of ADHD as the worst type of personal failings, so I think there's a level of trauma associated with growing up undiagnosed and being consistently blamed and shamed for things that were out of your control. Even without medication, getting diagnosed was, for me, the first step towards healing and starting to unpack all that shame.