I have actually completed hell. I've got no clue how long it took me from when I first discovered Cave Story, as I'm an on-off fan of it. (I'm a super big fan and play it nearly every day for a while, and then I slowly forget about it for a while, and then I remember and start playing again, and so on.)
My final time was 44'25"0, but I was taking forever doing the health respawn trick (by chance, I lost nearly all my health on the second chamber of Hell, on the playthrough I actually beat it on.
) and spending aaaages making sure I had as much health as I could for Ballos. Man, that was hard.
Trying to 3hp Doukutsu now, though. Stuck on Monster X last I tried, it was a while ago and I just came back to the game. (Had no idea it was Cave Story's birthday! Something must've called out to my soul...)