Cooking thick fresh egg pasta I tried making fresh egg pasta for the first time today, and generally I think the dough came out alright, except that, as I don't have a roller (and also because I just underestimated the thickness) my pasta was quite thick. I used 100g of 00 flour per large egg, that's all.

I essentially made what resemble tagliatelle but really think - I cut this by rolling out the dough into a rectangular sheet, folding inwards from both sides and then cutting through the rolls - quite a common technique I gained from watching videos.

My pasta came out a little hard, probably from the thickness, but I am unsure as to whether this means I should cook for more time or less time - I cooked for around 10 minutes.
Does hard pasta, given the thickness of my hand-rolled pasta mean undercooked or overcooked? Just trying to understand whether, other than rolling thinner, I need to cook for more or less time, next time.
The hardness you're experiencing is a sign that you've undercooked it. It isn't really "hard" in the sense that dry pasta is hard. It's not brittle, just very tough and difficult to bite through.

You can continue to cook it, but it's going to start becoming mushy on the outside before it becomes cooked through to the inside. That's why pastas are rolled out thin. Rolling it out thin with a rolling pin is enormous effort, so new pasta makers always give up too early. And they get this effect of tough pasta.

We all go through it. Stick with it. And then invest in a pasta roller, which makes it a bajillion times easier. But it's good to have done it the hard way a few times.