Yeah, that's a thing that I'm not worrying about much, because I don't want to fall in that trap which I have heard exists. I'm worrying about it about 2/3 as much as I should, though, and I'm going to get caught off guard by not having organized things like statblocks beforehand someday.
Right now about half my non-mechanics time is spent on cosmology worldbuilding, and half on small-scale cultures and creatures. This is a little silly, because cosmology is kind of irrelevant at 1st level.
On the other hand, as a player, I focused on mechanics and world approximately equally, so... eh, I d…