No matter how lengthy my writings get, each non trivial one takes about an hour or two to write. Its rather strange, as you would think it would scale linearly. I wrote a 3k (I initially remembered 30k, but that seemed outlandish) word email in about 2 hours, yet for the life of me I can't write a 500 word one in under an hour.
From my experience, the vast majority of the time spent "writing" is actually spent "thinking about what you want to write". Once you know what you want to write, the act of writing it down is comparatively trivial. So a short text may take the same amount of time as a longer one, as it is often harder to be concise with your words than it is to be liberal with them. Or perhapes correctly phrasing a short phrase takes just as much thought as correctly phrasing a long one.
Or in the case if my 3k word email, I already had known what I wanted to say, so it was just a matter of banging on the keys at 30 wpm and fixing errors.
It took me about 30 minutes to write this using my phone, and most of that was spent working through exactly what I wanted to say. Initially, this post was "I have this weird thing where it takes me the same amount of time to write long things and short things, I wonder why", but then I realised I had ideas as to why and thought it would be interesting to share. Then I was like "It would be interesting to get meta with this post", so then I did that, too.